A sum of Rs.10 is lent by a child to his friend to be returned in 11 monthly instalments of Rs.1 each, the interest being simple. The rate of interest is:

A

$$11\frac{9}{11} \%$$

B

$$21\frac{9}{11} \%$$

C

$$10\frac{2}{11} \%$$

D

$$9\frac{1}{11} \%$$