The boy             the bike, and it made his parents worried.[     ]

A. fell off  

B. fell down

C. fell from

D. fell

依据《社会保险法》规定，我国应建立（）社会保险制度。

A.基本养老保险

B.基本医疗保险

C.工伤保险

D.失业保险

E.生育保险