下列物质中属于含有非极性键化合物的是（      ）

科学兴趣小组为探究CO₂的多少是否会影响光合作用的强度，在家里做了如下的实验：

在某植物的叶片上剪下大小相同的多个叶圆片，抽出叶圆片中的气体（图如甲），然后，置于不同浓度的NaHCO₃溶液中（如图乙），测量每个杯子中叶圆片从杯底上浮至液面所需的平均时间．

注：NaHCO₃能增加溶液中CO₂的含量，叶圆片吸收CO₂释放O₂，部分O₂存在于细胞间隙和叶圆片边缘，导致叶圆片上浮．

    Three Things to Do Before You Are 18

    Are you bored with your daily life? Here are some things you should try before you are 18, because after that it's too late.

    ★Learn to swim

Seriously, this is so important that it can save your life. If you can't swim well, you won't be able to do water sports like waterskiing, surfing and diving. Even taking a boat trip will be dangerous for you. Make sure you do it.

    ★Try at least one kind of team sports

     Being a good team player is an important skill in life. You can't just think of yourself, but have to work well with other people. Other advantages(优点) of team sports like baseball are that they keep you fit and healthy, and they are also great fun. Teams usually have a good social life too--- you'll go to lots of parties and make many friends.

    ★Collect something

    One of the best hobbies for boys and girls under 18 is collecting things. You could collect kinds of stamps, or you could collect things that make you remember what you have done, like cinema tickets for films you have seen or emails from friends. The best way to collect is to have a special album(专辑) to put your collection in and to write what each thing means to you. That way you won't forget.

根据短文内容选择最佳答案