When writing test methods, what functionality is verified by the system method"runAs()"?

What feature in Salesforce is needed to restrict access to a custom object that has Public Read/Write access?

Users at Universal Containers are complaining that a field has disappeared from the Account page after deploying its latest project. The page layout has not changes with this deployment.
How should the admin troubleshoot this issue?

Universal Containers has built a recruiting application on the salesforce Platform. HR requested that all internal users should have edit access to the referral custom object. One of the recruiters needed to share a referral record with another colleague for collaboration using manual sharing. The recruiter opened the referral record and could not find the share button. What could be the technical reason for this?

Universal Containers (UC) implemented Sales Cloud and requested that only certain branch staff trained to sell high risk products can create opportunities for high risk products.
In which two ways can an Architect allow only specific branch staff to sell high risk products?
Choose 2 answers