What is true about the EoMPLS control word?

What is true about the EoMPLS control word?

A.
It is optional, but Cisco implementation never uses it.

B.
It is optional, but Cisco implementation always uses it.

C.
It is optional, and Cisco implementation uses it only whenever possible.

D.
It is required.

E.
There is no such a thing as EoMPLS control word.