【单选题】听力原文: Balloons have been used for sport for about 100 years. There are two kinds of sport balloons: gas and hot air. Hot air balloons are safer than gas balloons, which may catch fire. Hot air balloon...
【单选题】听力原文: Balloons have been used for sport for about 100 years. There are two kinds of sport balloons: gas, and hot air. Hot air balloons are safer than gas balloons, which may catch fire. Hot air balloo...