通过一年的学习,同学们对化学有了一些初步认识,你认为下列说法中不正确的是( )
A:自然界中的元素是有限的,但组成的物质却是无限的
B:宏观上相对静止的物体,其构成微粒也是静止的
C:物质都具有两面性,既可以造福人类,也可能造成危害
D:化学变化是有规律可循的,如化学变化往往伴随着能量的变化
等式x1-x=x1-x成立的条件是( )
I had a good time last weekend. On Saturday morning, I ____hiking with my mother. We climbed the mountain and ____ many pictures. For lunch, we ____ fresh fish in a restaurant. On Sunday morning, I played ____ with my cousin Sam. In the afternoon, I went____ on the lake. It was fun!
已知 ,CO和H2按物质的量之比1:2可以制得G,有机玻璃可按如图路线合成: