Explanation
According to the Salesforce documentation, the step type that would be used in engagement studio to add prospects to another engagement studio program's recipient list is an action. An engagement studio program is a feature that allows users to build, test, and report on automated programs that send targeted emails and perform actions based on prospect behavior and criteria. An engagement studio program consists of steps that define the logic and flow of the program. There are three types of steps: triggers, actions, and rules. A trigger is a step that checks for a prospect's activity, such as opening an email, clicking a link, or submitting a form.
An action is a step that performs an action on a prospect, such as sending an email, adjusting a score, or adding to a list. A rule is a step that checks for a prospect's attribute or value, such as score, grade, or field value. To add prospects to another engagement studio program's recipient list, the user can use an action step that adds prospects to a list. The user can then use that list as the recipient list for another engagement studio program. A rule, an end, or a trigger are not the step types that would be used in engagement studio to add prospects to another engagement studio program's recipient list, as they are related to other functions, such as checking for criteria, ending the program, or checking for activity. References: Salesforce documentation

Explanation
To test emails before sending them, the marketing team can use the test list feature in the testing tab of the email flow. This feature allows them to send test emails to a list of approved users who can view the links and variable tags as prospects will see them. The test list can be created in Marketing Cloud Account Engagement and added to the testing tab of the email flow. References: [Marketing Cloud Account Engagement Test List]

According to the Salesforce documentation, the "related" tab of the prospect record displays prospects that have the same score as the current prospect. The "related" tab is a feature that shows a list of prospects that are similar to the current prospect in Marketing Cloud Account Engagement. The "related" tab can be accessed from the Prospect Record page in Marketing Cloud Account Engagement, and it can show different columns of information for each related prospect, such as name, company, grade, score, or last activity. The user can customize the columns that are displayed on the "related" tab, and they can also sort, filter, search, or export the "related" tab. The "related" tab can also show other information for each related prospect, such as email address, title, assigned user, or custom fields, but these are not the default columns that are displayed on the "related" tab, and they need to be added by the user in the column settings. The "related" tab can help users to find and compare prospects that have the same level of interest and engagement as the current prospect, and to take actions based on the data. The "related" tab does not display prospects that have the same email domain, company, or assigned user as the current prospect, as these are not the criteria that are used to determine the similarity of the prospects. Reference: Salesforce documentation

If a marketing manager wants to view list email engagement metrics in Engagement History in Salesforce, they will not be able to see the Total Replies metric (A). This metric is not supported by Engagement History, which only shows the following metrics for list emails: Total Delivered, Unique Opens, Unique Clicks, Hard Bounces, Soft Bounces, Opt Outs, and Spam Complaints. The other metrics (B, C, D) are supported by Engagement History and can be viewed in Salesforce. Reference: Salesforce Engagement History: A Complete Overview

Explanation
According to the Salesforce documentation, the "related" tab of the prospect record displays prospects that have the same score as the current prospect. The "related" tab is a feature that shows a list of prospects that are similar to the current prospect in Marketing Cloud Account Engagement. The "related" tab can be accessed from the Prospect Record page in Marketing Cloud Account Engagement, and it can show different columns of information for each related prospect, such as name, company, grade, score, or last activity. The user can customize the columns that are displayed on the "related" tab, and they can also sort, filter, search, or export the "related" tab. The "related" tab can also show other information for each related prospect, such as email address, title, assigned user, or custom fields, but these are not the default columns that are displayed on the
"related" tab, and they need to be added by the user in the column settings. The "related" tab can help users to find and compare prospects that have the same level of interest and engagement as the current prospect, and to take actions based on the data. The "related" tab does not display prospects that have the same email domain, company, or assigned user as the current prospect, as these are not the criteria that are used to determine the similarity of the prospects. References: Salesforce documentation