维生素D缺乏性手足抽搐症的发病机制主要是（）。

A.甲状腺反应迟钝

B.甲状旁腺反应迟钝

C.垂体反应迟钝

D.肾上腺皮质反应迟钝

E.肾上腺髓质反应迟钝

His friends found_____ to tell him everything that had happened.

A．it necessary

B．that necessary

C．it is necessary

D．necessary