题目

在一定条件下，在一个密闭容器内发生某反应，测得反应过程中各物质的质量如下表所示，下列说法正确的是（）物质XYZW 反应前质量/g105200 反应后质量/g6.45待测6.4 A . W可能是单质 B . Y一定是催化剂 C . 该化学反应中X和W的质量变化之比是1：1 D . 反应后Z物质的质量为17.2g 答案：D阅读短文，选择最佳答案。I’m Yang Ming. I’m in Class One, Grade Four. There are forty students in our class. Twenty-one boys and nineteen girls. Today is Wednesday. We have six classes. They are Chinese, maths, music in the morning. English, PE, and Art in the afternoon. I like Chinese and PE. I’m good at reading and swimming.1. I’m in _____. ( ) A. Class 1, Grade 4 B. Class 4, Grade 42. There are ___ boys in our class. ( ) A.21 B.193. Today is ________. ( ) A. Tuesday B. Wednesday4. We have _____classes in the morning. ( ) A. 6 B. 35. I enjoy ___. ( )A. playing and doing B. reading and swimming