【简答题】Rewrite the following sentences on the basis of general principles of business letter-writing : We request the favour of a reply at your earliest convenience.
【判断题】气相色谱和液相色谱是根据固定相的状态来分类的。
【判断题】气相色谱法和液相色谱法是根据流动相的不同分类的
【单选题】Directions: Rewrite the sentences replacing the long expressions with single words selected from the accompanying list . The name of the sender could not be found in any part of the letter The letter ...