单项选择题

则a=(    )
   A.  B.7    C.      D.1

A.174.24.96:6088/Latex/latex.action?latex=XGJlZ2lue3ZhcnJheX0wICYgMCAmIDAgJjEgXFwwICYwICAmIGEgJiAwXFwwICYgMiAmMCAgJiAw%0D%0AXFwxICYwICAmIDAgJiBhXGVuZHt2YXJyYXl9PTE%3D'
B.C.174.24.96:6088/Latex/latex.action?latex=XGZyYWN7MX17Mn0%3D'
D.7
E.174.24.96:6088/Latex/latex.action?latex=LVxmcmFjezF9ezJ9'