Answer: Option D
$$\eqalign{
& {\text{Principal = Rs}}{\text{. 1000 }} \cr
& {\text{Rate = 5}}\% \cr
& {\text{Interest for first 10 years}} \cr
& = \frac{{1000 \times 5 \times 10}}{{100}} \cr
& = {\text{Rs}}{\text{. 500}} \cr
& {\text{After 10 years principal}} \cr
& = {\text{(1000}} + {\text{500)}} \cr
& {\text{ = Rs}}{\text{. 1500}} \cr
& {\text{Remaining interest}} \cr
& {\text{ = Rs}}{\text{. (2000}} - {\text{1500)}} \cr
& {\text{ = Rs}}{\text{. 500}} \cr
& {\text{Required time }} \cr
& {\text{ = }}\frac{{500}}{{1500}} \times \frac{{100}}{5} \cr
& = \frac{{100}}{15} \cr
& = \frac{{20}}{3} \cr
& = 6\frac{2}{3}{\text{ years}} \cr
& {\text{Total time}} \cr
& = \left( {10 + 6\frac{2}{3}} \right){\text{years}} \cr
& {\text{ = 16}}\frac{2}{3}{\text{ years}} \cr} $$