题目

下列关于酶的叙述，正确的是（ ）A.酶提供了反应过程所需的活化能B.酶既能作为催化剂，也可以是其他酶促反应的底物C.酶具有催化活性并且都能与双缩脲试剂反应呈现紫色D.酶在催化化学反应前后本身的性质会发生改变 答案：【答案】B【解析】酶是由活细胞产生的具有催化活性的有机物，其中大部分是蛋白质、少量是RNA；酶的特点：高效性、专一性、作用途径温和；酶的作用机理是降低化学反应的活化能。A、酶可以降低化学反应所需活化能，但是不能提供能量，A错误；B、酶是生物催化剂，其化学本质是蛋白质或RNA，因此听对话及问题，选择正确的答语。（对话读两遍，你有20秒钟的答题时间）(     )1. A. It's sunny. B. It's raining.  C. It's cloudy. (     )2. A. In a bank.  B. In a school. C. In a hospital. (     )3. A. Because she thinks it would be busy.            B. Because she thinks it would be exciting.            C. Because she thinks it would be interesting. (     )4. A. She is watching a movie.            B. She is going to the movies.            C. She is reading a book. (     )5. A. Because it's raining.            B. Because she wants to help her mother.           C. Because it's sunny.