老师说的没错：

Before you listen, you can read the questions and the choices.

=Before listening, you can read the questions and the choices.

听之前你可以先阅读问题和选项。

注意能这样改写的前提是从句主语与主句主语相同。又如：

Before making a decision (=Before you make a decision), you need to weigh up the pros and cons of the situation. 在作出决定之前，你需要权衡形势的利弊。

Before getting divorced (=Before you get divorced), you should think carefully about the effect it will have on the children. 离婚前，你应该慎重地考虑一下这将会给孩子们带来什么样的影响。

Before meeting with a client (=Before you meet with a client), you must try to erase any preconceptions you may have about them. 在和客户会面之前，应该尽可能消除任何有关他们的先入之见。

When singing this song (=When you sing this song), you stand in a circle, cross your arms over, and shake the hands of the people on each side of you. 唱这首歌时，你们站成圆圈，手臂交叉，与两旁的人拉手。

再以 when 举几个例子：

When preparing meals (=When you prepare meals), you need to think about variety and taste as well as nutritional value. 做饭时，你既需要考虑饭菜的营养价值，又需要考虑饭菜的花样和味道。

When driving on the highway (=When you drive on the highway), you need to make sure no one is in your blind spot before changing lanes. 在公路上驾驶时，你必须先确保视线盲区里没人，然后再变换车道。

When asking who you are speaking to on the phone (=When you ask who you are speaking to on the phone), you use the pronouns this in U.S. English and that in British English.打电话询问对方是谁时，在美国英语中用this，在英国英语中用that。