A:中和反应生成盐和水,所以生成盐和水的反应都是中和反应
B:盐是由金属离子和酸根离子组成的,所以盐中一定含有金属离子
C:向某固体物质中加入稀盐酸,生成无色无味气体,证明该物质一定是碳酸盐
D:碱性溶液能使酚酞试液变红色,所以能使酚酞试液变红色的溶液的pH一定大于7
如图示草原生态系统中的一条食物链,请据此判断下列说法是否正确.
—He ________ a model ship.
完形填空 I have a problem. Yesterday afternoon I 1 with my best friend, Kim. And he was very angry. I thought about it for a long time last 2. Now I know I was 3 at that time. But I don’t know 4should do. My mother thinks I 5 go to see Kim and tell him I was wrong. My father thinks I should 6 Kim and say 7 to him. And my brother 8 I should call Teen talk, the radio advice program. My sister tells 9 I should call up my teacher for 10.Can you tell me what I should do?
与原始大气相比,现代大气中的氧气的产生主要是来源于