英语单选题,请解析并判断其他句错的原因

英语单选题,请解析并判断其他句错的原因
5道高中英语单项选择,
1The boy student is poor in health now his parents wish that his health ___when he grows up A． could improve B．can be improved
2．-I'm interested in that beautiful MP4 player．How much do you charge for it?
-$ 150．And it's of the value．
-Well,___．but I can't afford it．Thank you anyway．
A．it's really nice B．it's worth that
3-How I wish I ___ hard when I was in high school-If you had,you would be in a good university now．
A．had studied B．could have studied
4 With so many people ___ in the mine,none of the rescue workers would stop to have a rest.A．buried B．being buried
5A good amount of sleep every night important for your body to prepare you for ___ day to come.
A．the B．A
怎么这些选项都应该选A,请写出如何排除B选项的
还有第二题正确答案应该是选B,那其他选项都错在哪,