“或”门电路的逻辑表达式为（）。
A.Y=A²B
B.Y=A+B
C.Y=A-B
D.Y=A÷B
参考答案：B
John promised his doctor he ________ not smoke, and he has never smoked ever since. [ ]
A. might
B. should
C. could
D. would
在胎儿时期，能通过胎盘的免疫物质是：（）
A.IgM
B.补体
C.IgA
D.IgG
E.母亲的淋巴细胞
