必须保持

• It also means that the quantity of a given chemical entity not destroyed by the reaction must remain constant .
  它还意味着已知化学物质的量不但不会被反应所改变而且必须保持恒定。
• Law must be stable and it cannot stand still
  法律必须保持稳定但却不能一成不变
• In the presence of danger , we must keep calm
  在面对危险时，我们必须保持冷静。
• We must keep silent while others are studying
  当别人学习时，我们必须保持安静。
• It must keep the news comprehensive and proportional
  新闻必须保持全面和均衡。
• When you are in a library , you must be quiet
  当你在图书馆时，你必须保持安静。
• Go and buy yourself something nice . go watch a movie
  你必须保持定力，临崖勒马。
• Law must be stable and it cannot stand still
  法律必须保持稳定，也不能一成不变。
• In all cases traceability must be maintained
  在所有情况下都必须保持可追溯性。
• First of all understand you have to be alert
  首先要明白一件事，你必须保持敏锐。