Mr. Black ________ for Shanghai in a few days. Do you know when the earliest plane ________ on Sunday?

A．leaves; takes off

B．leaves; is taking off

C．is leaving; is taking off

D．is leaving; takes off

佝楼病是婴幼儿缺钙的病症，维生素 D可促进机体对钙的吸收，所以给病人补充足量的钙和维生素D，维生素 D的主要作用是

A．促进小肠对钙磷的吸收，促进肾小管对钙磷重吸收
B．刺激肝脏25α羟化酶合成，抑制 24a羟化酶合成
C．抑制骨髓钙结合蛋白合成，抑制破骨细胞活性
D．加快肝脏钙调蛋白降解，促进细胞摄取血钙
E．促进成骨细胞摄取血钙，降低血钙浓度