烧结矿的气孔率越高，越有利于还原，因而质量越好。
参考答案：错
— Have you ever been to Xiushui No.1 High School?
— No. It is the first time that I ______ to Xiushui. [ ]
A. come
B. have come
C. am coming
D. came
孕妇做产前血清学筛查最佳时间是：（）
A.孕10—12周
B.孕16—20周
C.孕20—24周
D.孕26—28周
