How was the trip?It must be very tiring ,flying for more than 10 hours英语问题

题目

How was the trip?It must be very tiring ,flying for more than 10 hours英语问题
flying for more than 10 hours是个什么丛句,为什么用flying呢?那不是已经 过去的事情了吗?

答案

这个flying不是表示动词的现在进行时,而是动词的现在分词,做句子成分,应该是主语,flying for more than 10 hours must be very tiring,用it做主语,把这个后置了.
不是所有动词的ing形式都表示现在进行时的.