如果|a|+|b|=0则a与b的大小关系一定是[ ]
A.a=b=0
B.a与b不相等
C.a与b互为相反数
D.a与b异号
答案：A
— I failed the history test. — [ ]
A. I'm sorry to hear that.
B. You are luck.
C. I see.
母猪胚胎死亡的原因有哪些？如何提高胚胎的成活率？
