Sue just turned age $65.$ She is still working and is covered under her employer's group health plan. Which one of the following is a true statement regarding her enrollment in Medicare?

A$)$

Following termination of employment she can only enroll in Medicare without penalty during the following "general enrollment period."

B$)$

She is required to enroll in Medicare during the $60-$day period following termination of employment.

C$)$

She will be assessed a $10\%$ penalty for every $12-$month period during which she could have enrolled in Medicare but didn't.

D$)$

Following termination of employment she will be granted an eight$-$month "special enrollment period" during which she can enroll in Medicare without penalty.