What is true about the label in frame-mode MPLS?

What is true about the label in frame-mode MPLS?

A.
32 bit label with an 8 bit label field.

B.
32 bit label with a 20 bit label field.

C.
20 bit label with a 3 bit Bottom of Stack field.

D.
20 bit label with a 1 bit TTL field.