一道英语题请求解析Could you please give me your e-mail address --- yo

一道英语题请求解析Could you please give me your e-mail address ___ you go ?答案是before,为什么不用after?你们好，非常感谢你们的帮助，这些题困扰了我很久，百思不得，只好向各位求助了，在此先谢了。加十分！！！Ads sometimes help people learn more about new prouducts,but at other times ads ___ tell lies.a.must b.can c.need d.should答案是b,请问为什么？I've never ____ him before.a.heared to b.heared of答案是b,请问为什么？--What's your speech ___,Dr.Smith?--Tomorrow you will get it.a.by b.of c.from d.on答案是on ,为什么？Class 2 will go for a picnic.They made ___ 6 o'clock to meet at the foot of Mr.Tai.a.it b.that c./答案是a,为什么？