Research shows that readers are most attentive at the beginning and end of a piece of writing. This means that if you are going to have maximum impact in getting people to agree with you (or give you a good mark), you need to put some effort into these two parts of your essay. If you basically repeat the question you have been set for an introduction and then serve it again at the end, it will be like a meal with the same dish served two or three times: dull.
However, in a straightforward discussion essay in which you have argued a position, your conclusion is your opening thesis or something has gone wrong. In this case, you are going to repeat your idea, but you can dress it differently. A lot of the ingredients of dim sum are the same, but they are put together in different ways to create different flavours. Try to re-express yourself.
It is rather neat and satisfying if your essay can come full circle and your conclusion in some way return to your opening. If you started with a question, you can point out that now you have an answer.
What will happen if global warming continues?
Now we can see that the answer to our opening question is bleak: there will be no more Hong Kong. That is something for us all to think deeply about. This not only circles around, but it personalises by making the reader realise they will be affected. It also has not just a conclusion, but a clear end in those final words. When you read them you know the writer has finished.
Another example of returning to the start would be if you began with a description or story. You can then finish that or produce a contrasting version. An essay on education reforms might begin with a description of stressed students writing as fast as their arms can move in a traditional paper and pen examination.
