In the PostgreSQL implementation, users and roles are exactly the same: CREATE USER and ALTER USER internally execute CREATE ROLE and ALTER ROLE. What they can do is exactly the same.

CREATE USER/ROLE allows you to create a new user role and specify attributes such as privileges. ALTER USER/ROLE does not allow you to create new user roles, but it does allow you to change the attributes that can be specified in CREATE for existing user roles. Attributes that can be specified or modified by CREATE or ALTER include password, whether or not the user has permission to create users, whether or not the user has permission to create databases, and whether or not the user is a superuser (administrator user).

Access to individual objects, such as tables, is granted with GRANT, not ALTER USER/ROLE.

So the correct answers are B, C and D.