A CFG(Context Free Grammar)is said to be in Chomsky Normal Form (CNF),if all the productions are of the form $$A \rightarrow BC$$ or $$A \rightarrow a$$. Let G be a CFG in CNF. To derive string of terminals of length x, the number of products to be used is

A

$$2x - 1$$

B

$$2x$$

C

$$2x + 1$$

D

$$2^x$$