Please help with this question.

Question

Insulin, antibodies, enzymes and progesterone are four of many molecules found in and around cells. Of these four__________ are/is not a protein.

a. antibodies
b. insulin and antibodies
c. antibodies and progesterone
d. progesterone

I think the answer is "A" but am not sure. please help

progesterone does not contain nitrogen: proteins are nitrogenous compounds. Antibodies are proteins.

Answer 1

Progesterone.