Stamp collection has long been recognized as having an educational value. There is every reason to encourage young people to take an interest in them, thereby ______ to their knowledge of geography and history.

A．to add

B．adding

C．added

D．adds

雄激素不敏感综合症是指

A．真两性畸形
B．男性假两性畸形
C．女性假两性畸形
D．混合性生殖腺发育不全
E．单纯型生殖腺发育不全