题目

（1）在做体育训练拉单杠时，体育老师给小明使用了“镁粉”（主要成分是碳酸镁），碳酸镁的化学式为MgCO3，求碳酸镁的相对分子质量是 ，碳酸镁中镁元素、碳元素和氧元素质量比是 ，碳酸镁中镁元素的质量分数是 ．（保留小数点后一位） （2）8.8克二氧化碳中氧元素质量和多少克碳酸镁中氧元素相等？（列式求解） 根据对话内容。从对话后面的选项中选择五个正确的句子，完成下列对话。 A．You're welcome. B．That's right. C．What's the time? D．I can't have breakfast. E．Who are you?F．What are you late for? G．It's Sunday today. Tom: Really? 1.            Bob: It's about 7:30. Tom: What? It's 7:30 now. I must get up. I'm late.Bob: Oh,Tom, wait. Just sit down and have, breakfast. Tom: 2.             There's no time, you know. I'm late.Bob: 3.             Tom: For school. You see. Classes begin at 8:00. Bob: Well don't worry. What day is it today? Please tell me.Tom: It 4.            (Tom laughs.)Bob: Oh, 5.            So just sit down and have breakfast with me. (Bob laughs, too.)