引起继发性甲状旁腺功能亢进的重要环节有()
A.高血磷、低血钙
B.低血磷、高血钙
C.高血磷、高血钙
D.低血磷、低血钙
E.活性维生素D3缺乏
参考答案:A, E
Because the old people ________ about thirty percent of the population, we should care more about them.
A.look up
B.fix up
C.make up
D.end up
若D1=a1,a2,a3,D2=b1,b2,b3,则D1×D2集合中共有______个元组。