18、 Therefore, we should not only...but...as well.
例句:Therefore, we should not only realize that competition and cooperation, like two sides of the coin, have to go hand in hand, but fix more attention on how to make full use of cooperation as well.
19、In short, ...are the major problems to be solved to...
例句:In short, shortage of water, decrease of fertile fields and environmental pollution are the major problems to be solved to increase grain production.
20、Who is to say that...?
例句:Who is to say that our scientists may not provide a better theory?