工业上用分离液态空气的方法制取氧气，是利用了液氮和液氧的____ 不同．

—Sorry，sir．But it is the management rules of our hotel that payment _____ be made in cash．

注意：1)发言稿须包含上述要点,但可适当发挥,使讲话完整通顺。

      2)100词左右。

Dear classmates,

    It's a pleasure for me to have a chance to make a short speech today.