3道高一英语选择题1、He saw a boy and his cow ____ were gong down the

3道高一英语选择题
1、He saw a boy and his cow ____ were gong down the hill.
A.which
B.who
C.that
D.with which
选C,Why?
2、It was five o'clock in the afternoon____ they arrived at the hotel.
A.since
B.before
C.that
D.when
选D,为什么不选C呀?
3、The hours ____ the children spend in one-way relationship with television people un doubtebtedly affect their relationship with real-life people.
A.in which
B.on which
C.when
D.that
也选D,为什么不选C?

哪位大神肯详细讲讲?太谢谢了!