Consider a simple circuit shown in the figure. R' stands for variable resistance. R' can vary from ${\mathrm{R}}_{\mathrm{o}}$ to infinity. r is the internal resistance of the battery (r<<R<<R).

(a) Potential drop across AB is nearly constant as R' is varied
(b) Current through R' is nearly constant as R' is varied
(c) Current I depends sensitively on R
(d) $\mathrm{I} \ge \frac{\mathrm{V}}{\mathrm{r}\hspace{0.17em}+ \mathrm{R}}$

Which among the following statements is correct?

1. (a, c)

2. (a, d)

3. (b, d)

4. (c, d)