The rate of radioactive disintegration at an instant for a radioactive sample of half-life $2.2\times 10^9\text{s}$ is $10^{10}{\text{s}}^{-1}$. The number of radioactive atoms in that sample at that instant is:

1. A
   $3.17\times 10^{20}$
2. B
   $3.17\times 10^{17}$
3. C
   $3.17\times 10^{18}$
4. D
   $3.17\times 10^{19}$