请选择并作详细解释
1 Reading English magazines and newspapers---helpful to your study of English.
A is B are C will D is going to do
2 He wanted to know how long --- there.
A I had been B had I been C I have been D have I been
3 You can not leave until you --- your homework.
A finished B will finish C would finish D have finished
4 The young man---.
A hold his breath B held his breath
5 How long --- at the factory?
A have you come B has he in C will he be D has he been to
6 Our workshop ---since two years ago.
A was open B opened C has been open D has opened
7 His hair---white these days.
A be B are C has turned D turned

1、阅读英语杂志和报纸对你学习英语有帮助
用are，选B

2、他想知道我在那里多长时间了。
前面用的是过去时，而句子的意思问的是一个持续的时间，所以用过去完成时，选A

3、你什么时候写完作业，什么时候才能离开。
finish不是一个持续性的状态，不能用D，B和C也不对，只有A对。

4、这个男人屏住了呼吸。
这个是最没什么说的，又没有限定时态，选A肯定不行。

5、问的是在工厂多长时间了，是完成时，只有D正确。

6、有since，前面就一定是完成时，选D。因为C是被动语态，而open的过去分词加ed，这里用原形，所以不对

7、他的头发这几天变白了。
A、B肯定不对，而这又是一个持续性的，所以D也不对，只能是C。完成时