Consider a simple circuit shown in fig 

stands for a variable resistance R'. R' can vary from R0 to infinity. r is internal resistance of the battery $\left(\mathrm{r}<<\mathrm{R}<<{\mathrm{R}}_0\right)$ 

a) Potential drop across AB is nearly constant as R' is varied.  

b) Current through R' is nearly a constant as R' is varied. 

c) Current I depends sensitively on R'

d) $\mathrm{I}\ge \frac{\mathrm{V}}{\mathrm{r}+\mathrm{R}}\text{ always }$