问题
选择题
Fu Mingxia _____ a lot of gold medals since 1996.[ ]
A. wins
B. won
C. is winning
D. has won
答案
D
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Fu Mingxia _____ a lot of gold medals since 1996.[ ]
A. wins
B. won
C. is winning
D. has won
D
，求常数a；
的数学期望．