简述动物精液冷冻技术的基本流程。
参考答案：
采精→精液品质坚定→稀释液配制→稀释→降温→平衡→冷冻→保存。
如果集合A={x|x2+ax+1=0}中只有一个元素，则a的值是（ ）
A．0
B．0或2
C．2
D．-2或2
My uncle ______ until he was forty-five . [ ]
A. married
B. didn't marry
C. was not marrying
D. would marry
