当体内（）等维生素缺乏时，易引起高同型半胱氨酸血症。

A.维生素B₆

B.维生素B₁₂

C.维生素A

D.叶酸

E.维生素K

5. --- Why didn’t Tom give you one of his paintings?

--- I didn’t want one, but he would have given me one if I______.

A．did

B．would

C．will

D．Had