If m divides $$a - b$$, then we write $$a \equiv b$$ (mod m).Then the correct statement among the following is

A

$$2^{15} = 4$$(mod 7)

B

$$2^{17} = 3$$(mod 7)

C

$$2^{20} = 2$$(mod 7)

D

$$2^{24} = 1$$(mod 7)