There are so many kinds of MP5 in the shop. We can not decide _____.[ ]

A. what to buy

B. to buy what

C. which to buy

D. to buy which

男孩，3岁。尚不会独立行走，智力亦落后于同龄儿。

可能的诊断是（）

A.先天性甲状腺功能减低

B.21-三体综合征

C.苯丙酮尿症

D.粘多糖病

E.软骨发育不良

F.脑发育不全

G.佝偻病