不影响双磁路磁珠法进行凝血测试的因素是（）。

A.凝血激活剂

B.纤维蛋白的量

C.溶血

D.黄疸

E.高血脂症

There _____ many kinds of birds around here,

but now we seldom see them because of the air pollution. [ ]

A. use to

B. use to have

C. used to be

D. are