（1）天然气是一种清洁高效的能源，其主要成分为甲烷．CH₄的摩尔质量为　 ____　，4.8gCH₄的物质的量为　 ____　，在标准状况下的体积约为　 ____　，所含氢原子数为　 ____．

（2）某化学兴趣小组对某矿泉水进行检测，发现0.5L该矿泉水中含有10.8mgMg²⁺，则Mg²⁺的物质的量浓度为　 ____　．

（3）体积比为1：2：3的氯化钠、氯化镁和氯化铝溶液，分别加入等体积、等浓度的硝酸银溶液，均恰好完全反应生成氯化银沉淀，则这三种溶液的物质的量浓度之比为 ____

（A）

Some Advice on Travel

1)．Forget about fashion．Always wear your most comfortable clothes when going on long journeys（旅行）．

2)．Traveling on trains and buses can be boring, so take a good book to read．

3)．If you're going somewhere cold, remember to take your warm clothes．

4)．If you're going somewhere sunny, remember to wear sunblock（防晒霜）and sunglasses．

5)．Always take a camera with you to capture those special moments．

6)．Be careful with your things whenever you go to busy places, like a train station．There are often thieves there!

7)．Always leave room in your bag for presents．

8)．Most countries have lower prices for students, so if you have one, take your student card with and save money．

在反应2A+B=3C+D中，A和B的相对分子质量之比为5：2，已知20g A与一定量B恰好完全反应，生成10g D，则在此反应中生成C的质量为（   ）

如图，已知∠AOB．小明按如下步骤作图：

（1）以点O为圆心，适当长为半径画弧，交OA于D，交OB于点E．

（2）分别以D，E为圆心，大于$\frac{1}{2}$DE的长为半径画弧，两弧在∠AOB的内部相交于点C．

（3）画射线OC．

根据上述作图步骤，下列结论正确的是（　　）

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