If you often feel tired and can’t focus
题型：选择题
问题：
If you often feel tired and can’t focus your attention，that is________you have to stop working too
hard and to have a rest.[ ]
A．why
B．whether
C．when
D．what
If you often feel tired and can’t focus your attention，that is________you have to stop working too
hard and to have a rest.[ ]
A．why
B．whether
C．when
D．what