—Tomorrow ___ my birthday, I’d like you and Jane to come.

-- I’m not sure if she ____ free.

A．will be; is going to

B．is going to; is

C．will be; is

D．is; will be

钠的主要生理功能是（）.

A.维持酸碱平衡

B.钠泵

C.增强神经肌肉兴奋性

D.调节体内水分与渗透压