Explanation/Reference:
Explanation:
How Permissions Are Checked in a Chain
When an object is accessed through a chain, SQL Server first compares the owner of the object to the owner of the calling object. This is the previous link in the chain. If both objects have the same owner, permissions on the referenced object are not evaluated.
Due to ownership chaining, you would only need to give Execute permissions to UserC to access the Orders table since UserB is the owner.
You would also need to assign Select permission on the Customers table, as it is owned by UserA.
References:
https://technet.microsoft.com/en-us/library/ms188676(v=sql.105).aspx