桥面上通过的风管、水管必须捆牢，不得侵入限界。（）
参考答案：对
--- What do you often do_______ classes to relax yourselves?
--- We often do eye exercises, listen to music or do some running around the school.
A．in
B．among
C．between
D．during
凡是由外界环境改变引起的变异不可遗传．______．
