调查法的研究对象可来源于志愿者。
参考答案:错
It is dangerous to allow the children who are ________ swimming in the river.
A.enough old to go
B.not old enough to go
C.not enough old to go
D.not old enough going
其实,“开始”菜单是一个集中了很多快捷方式的( )。
A.文件B.文件夹C.对象D.程序