The sum of coefficients of $\mathbf { x } ^ { \mathbf { 4 9 9 } }$ and $\mathbf { x } ^ { \mathbf { 5 0 0 } }$ in the binomial expansion of $( 1 + x ) ^ { 1000 } + ( 1 + x ) ^ { 999 } ( x ) + x ^ { 2 } ( 1 + x ) ^ { 998 } + \cdots + x ^ { 1000 }$ is
(A) ${ } ^ { 1002 } \mathrm { C } _ { 501 }$ lool terms
(B) ${ } ^ { 1001 } \mathrm { C } _ { 501 }$
(C) ${ } ^ { 1001 } \mathrm { C } _ { 500 } \quad \gamma = \frac { x } { 1 + x }$
(D) ${ } ^ { 1002 } \mathrm { C } _ { 500 }$