题目

下列物质中有几种属于氨基酸，若这几种氨基酸缩合成化合物，则其中含有氨基、羧基、肽键的数目依次是                                                  COOH                                                  | ①NH2－CH2－COOH      ②NH2－CH2－CH2OH      ③NH2－CH－CH2－COOH        NH2                       COOH        |                         | ④NH2－CH－CH2－COOH       ⑤7. We must try our best to stop the pollution . (live) a happy life.