正常胎心每分钟应在（）次左右。
A.100
B.140
C.160
D.180
参考答案：B
There’s _____ wrong with my chair. Can you mend it? — No problem.
A．something
B．nothing
C．everything
D．anything
琼脂糖凝胶分离DNA的原理是电泳迁移率与DNA分子的相对分子质量相关。( )
