Would you please explain it again? 请你再解释一遍可以吗？
Can you follow me? 你们能跟上我讲的吗？
Your answer is correct. 你的答案是正确的。
Class is over in five minutes. 还有5分钟就下课了。
Let's call it a day. 今天就上到这里。
The reagent is not the right for this experiment. 这个试剂不是这个实验用的。
Have you read the instructions? 你阅读说明书了吗？
Do we have homework today? 你今天有作业吗？
