The two actions that can cause an anonymous visitor to convert into an identified prospect are submitting a form on a landing page and clicking on a tracked link in an email. An anonymous visitor is a person who visits your website or interacts with your marketing assets, but whose information you have not captured in Marketing Cloud Account Engagement. An identified prospect is a person whose information you have captured in Marketing Cloud Account Engagement, and whose activities you can track and measure. You can convert an anonymous visitor into an identified prospect by capturing their email address, which is used as the unique identifier for the prospect record. You can capture the email address of an anonymous visitor by:
Submitting a form on a landing page. A form is a web element that allows you to collect information from your visitors, such as their name, email, or company. A landing page is a web page that you create and host in Marketing Cloud Account Engagement to showcase your products or services, offer content, or register for events. You can add a form to a landing page to capture leads or convert visitors into prospects. When an anonymous visitor submits a form on a landing page, Marketing Cloud Account Engagement will create a new prospect record with the information provided by the visitor, and associate the previous activities of the visitor with the prospect record4.
Clicking on a tracked link in an email. A tracked link is a link that is modified by Marketing Cloud Account Engagement to track the click activity and redirect the visitor to the original URL. You can use tracked links in your emails, social media posts, or banner ads to measure the engagement of your visitors with your online marketing content. When an anonymous visitor clicks on a tracked link in an email, Marketing Cloud Account Engagement will append the email address of the visitor to the URL, and use it to create a new prospect record or update an existing one. Marketing Cloud Account Engagement will also associate the previous activities of the visitor with the prospect record.

Explanation
If a LenoxSoft marketer selects the option "Redirect the prospect instead of showing the form's Thank You Content" when creating a new Account Engagement landing page, the expected behavior when a prospect submits a form designed to show Thank you Content is that the prospect will be redirected to another webpage. This option overrides the form's Thank you Content and sends the prospect to the specified URL instead.
The prospect will not continue to see the form upon submission (A), nor will the discrepancy between the two assets cause an error (B). The form's Thank you Content will not display (D), as it is replaced by the redirect option. References: Redirect Account Engagement Forms to a Success Page

If a form is added to a landing page, the submissions will be reported on the form. A form is a web element that allows you to collect information from your prospects, such as their name, email, or company. A landing page is a web page that you create and host in Marketing Cloud Account Engagement to showcase your products or services, offer content, or register for events. You can add a form to a landing page to capture leads or convert visitors into prospects. When a prospect submits a form on a landing page, the submission data will be recorded on the form report, which shows you the number of views, submissions, errors, and conversion rate of your form

Explanation
The daily system generated emails are: daily prospect activity emails (for all prospects), daily prospect activity emails (for my prospects), daily visitor activity emails, and daily prospect assignment emails. These are the emails that Marketing Cloud Account Engagement sends to users based on their preferences, which provide a summary of the activities and actions of prospects and visitors on a daily basis. Daily prospect activity emails (for all prospects) show the activities of all prospects in your Marketing Cloud Account Engagement account.
Daily prospect activity emails (for my prospects) show the activities of the prospects that are assigned to you.
Daily visitor activity emails show the activities of the anonymous visitors on your website. Daily prospect assignment emails show the prospects that have been assigned to you or to other users910 References: 9: Auto generated email - How to guide10: Customizing the System Generated Emails

Explanation
According to the Salesforce documentation, the two capabilities that are true for completion actions are: C) Completion actions cannot be applied directly on a landing page, and D) Completion actions do not execute on image file downloads. A completion action is an automation tool that can be used to perform an action after a prospect successfully completes a marketing element, such as clicking a link in an email, submitting a form, or visiting a web page. A completion action can be used to perform actions such as adding a prospect to a list, assigning a prospect to a user, sending an autoresponder email, or adjusting a prospect's score. Completion actions cannot be applied directly on a landing page, as landing pages do not have completion actions.
However, completion actions can be applied on the forms or custom redirects that are embedded on the landing page. Completion actions do not execute on image file downloads, as image file downloads are not considered as completion events. However, completion actions can be executed on other types of file downloads, such as PDFs or Word documents. Completion actions are not applied retroactively, as they are only applied to prospects who complete the marketing element after the completion action is created.
Completion actions do not apply to both visitors and prospects, as they only apply to prospects who have been identified by their email address or their Marketing Cloud Account Engagement tracking cookie.
References: Salesforce documentation