下列有关叙述不正确的是（　　）

A．人体缺铁会引起贫血

B．老年然缺钙会发生骨质疏松，容易骨折

C．缺碘会导致人的甲状腺肿大

D．人体摄入微量元素越多越好

Some people get in touch with each other by mobile phones__________ others keep contact with each other by e-mail.

A．when

B．before

C．while

D．since