【简答题】What enabled the earliest balloons to fly? [A] Gas produced by metal and coal. . [B] Air kept hot by burning coal. [C] Hydrogen heated by a. gas burner. [D] Natural gas carried in a metal container.
【简答题】小题1:.. You can find out the reason for this f__________ (失败). 小题2:.. No one can a__________ (取得成就) anything without effort. 小题3:.. That rich man has a large staff of s__________ (仆人). 小题4:.. He made a...