Which of the following statement(s) is/are correct. Here a and $r$ have their usual meaning:

(A) $a, ar, ar^2, ....$ is a G.P.
(B) $n^{th}$ term of a G.P. is $a_{n}=ar^{n-1}$
(C) $n^{th}$ term of a G.P. is $a_{n}=ar^{n+1}$
(D) Sum of first $n$ terms of a G.P. is $S_n=a\left(\frac{r^n-1}{r-1}\right), r \neq 1$
(E) $1,4,16,256, ....$ is a G.P.

Choose the correct answer from the options given below:

(A), (B) and (D) only

The correct answer is Option (4) → (A), (B) and (D) only

Here, Formulas given in the option (A), (B) and (D) are correct.