伤寒发病第1周内，阳性率最高的化验是( )
A．血培养B．粪培养C．尿培养D．肥达反应E．以上都不是
参考答案：A
染色体非整倍性改变的机制可能是（）
A.染色体断裂
B.染色体核内复制
C.染色体倒位
D.染色体不分离
E.染色体融合
Directions:
Study the following picture carefully and write an essay to
1) describe the picture briefly,
2) deduce the purpose of the drawer of the picture, and
3) suggest counter-measures.
You should write about 160--200 words neatly on ANSWER SHEET 2.
