How many naturally occurring amino acids are used by ribosomes to construct proteins?

Question

a) 10

b) 20

c)46

d) 64

e) 3

I think its 20, but I need some verification on that

Answer 1

20

Answer 2

b) 20

is the answer your teacher wants.

It's pretty close to correct.  In prokaryotes, there're actually 21, since chain initiation starts with formylmethionine instead of methionine.