题干

在学习了呼吸系统的知识后,某科学兴趣小组的同学为了证明人体呼出的气体中含有较多的二氧化碳,根据“二氧化碳具有使澄清石灰水变浑浊的特性”设计了以下实验:

材料用具:澄清石灰水、试管2支、气球2个、打气泵1个、凡士林、细线若干条。

设计方案:

步骤一:把气球A吹到一定大小,并用细线扎紧气球口,接着用打气泵向气球B打入空气,使其与气球A一样大,也扎紧气球口。

步骤二:向甲、乙两支试管中分别加入3毫升澄清石灰水。

步骤三:在甲、乙试管外壁涂上凡士林,减少实验时气体外泄。

步骤四:把气球A和B分别套在试管甲和乙上(如图所示),解开气球,将球内气体通入试管,并轻轻振荡。

步骤五:观察甲、乙试管内石灰水的变化。

根据以上实验设计,回答下列问题。

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