spend some time doing

To prepare for the listening test, you should spend some time doing questions from past NETEM and Band 6 listening exams.

对于听力测试的准备，你们应该花费一些时间做NETEM和6级的听力考试题。

When you wait for something or someone, you spend some time doing very little, because you cannot act until that thing happens or that person arrives.

当等待某人或某事时，你长时间无所适从，无所事事，因为在某事发生或某人到来之前你素手无策！

In fact, I highly recommend if you get involved in using WEKA on your server, you spend some time doing that, since working with data in this way is tedious.

实际上，我强烈建议如果打算在服务器上使用WEKA，那么就不要怕花时间，因为以这种方式处理数据是很繁琐的。