The value of $(^{21}C_1 - ^{10} C_1) +(^{21} C_2 -^{10}C_2) +(^{21}C_3 - ^{10} C_3) +(^{21}C_4 - ^{10} C_4) +.....+ (^{21}C_{10} - ^{10} C_{10})$ is :

Question

$\begin{array}{1 1} (1) 2^{ 21}−2^{10} \\ (2) 2^{20}−2{9} \\ (3) 2^{20}−2^{10} \\ (4) 2^{21}−2^{11} \end{array}$