He goes to school by bus, but __________ after school.

A．walk home

B．walks to home

C．on foot home

D．walks home

维生素D结构中活性最强的一项是()

A．胆骨化醇

B．25-羟胆骨化醇

C．1,25-二羟胆骨化醇

D．24,25-二羟化醇

E．麦角骨化醇