Who would use claim code $"0"$ on the federal TD$1$ form?

Question $1$ options:

Employees with earnings in excess of the maximum amount listed in the federal claim codes

Employees with total insurable earnings that are less than their basic personal tax credits being claimed

All part$-$time students working summer jobs and having earnings less than the basic personal tax credits

Non$-$resident employees and employees working other jobs and already claiming the basic federal tax credits