If OWD is Public Read Only, what are sharing access options

Universal Containers has a strict security model enforced through object, field, and row-based security mechanisms. The Architect would like to ensure the security model is being thoroughly tested using Apex automated tests. Which three considerations should be made when using the runAs() method to design Apex until tests?

If you want to create some logic that will share certain records in APEX code, you just have to create special records that will open access to the desired records.
The aim is to create records of certain type, for example , all share objects for custom objects are named as ___________?

Cloud Kicks imports large-volume bulk data loads and wants to limit the risk of failures associated with these imports.
What are two options for achieving this goal? (Choose two.)

A sales rep (John) at Universal Containers (UC) requested to update information in an account record where he has READ only access. John requested the EDIT access permission from the owner of the record (Paul). Paul manually shared the record with John. Assuming the OWD of the Account object is Public Read-Only, what is the impact in the system?