During the entrance (升学) exams, there are______ parents waiting for their children outside their test center.[ ]

A. thousand of

B. thousands of

C. thousand

D. thousands

与骨骼生长发育关系最密切的是（）。

A.维生素B1

B.维生素C

C.维生素E

D.烟酸

E.维生素D