根据以下资料回答第39、40题。
There is an old Chinese saying, "If someone gives you a little drop of water, you shouldreturn a spring of water." That means if someone helps you a bit, you should remember it and thankthem in return. 
We should live in a world of gratitude. We should prove it with actions, not just words. Wethank people who hurt us, because they teach us important things. We thank people who give usup, because we learn how to be independent. We thank people who are selfish (自私的), becausewe learn the importance of being kind. Of course, we should thank people who help us. We shouldthank people who teach us. We should thank people who care about us. 
We thank our parents. They work hard all the time in order to give their sons and daughters abetter life. They cook meals for us; they do the chores for us; they always give us food and clothes;they teach us what is right and what is wrong. 
We thank our teachers who give us dreams. They teach us a lot of things but they ask fornothing from us. We are well-educated by them. 
There are a lot of people that we should be grateful to in our life. We should find a way to thankthem.
According to the writer, you should________ if someone helps you.