先天性心脏病致病遗传因素有（）
A.单基因突变
B.多基因突变
C.染色体畸变
D.代谢疾病
E.宫内感染
参考答案：A, B, C
V．P试验呈阳性反应的指示颜色是红色。
_—Did you visit the Summer Palace?
—No.We could have, _______we spent too much time shopping.
A.so B but C.ecause D.though
