抑制核苷酸还原酶的抗恶性肿瘤药物是（）
A.羟基脲
B.阿糖胞苷
C.甲氨蝶呤
D.氟尿嘧啶
E.巯嘌呤
参考答案：A
His father was in poor health and had to give up _____.[ ]
A. smoke
B. to smoke
C. to smoking
D. smoking
哪个时期服用四环素类药物可致恒牙发生四环素牙（）
A.胚胎4个月
B.胚胎7个月
C.出生以前
D.出生至7岁以前
E.8岁以后
