The value of $(^{21} C_1 - ^{10}C_1) + (^{21}C_2 - ^{19}C_2) + (^{21}C_3 -^{10}C_3) + (^{21}C_4 - ^{10}C_4) +...+(^{21}C_{10} - ^{10}C_{10})$ is

Question

( A ) $2^{21} - 2^{11}$
( B ) $2^{21} - 2^{10}$
( C ) $2^{20} - 2^{10}$
( D ) $2^{20} - 2^{9}$