will he fly to Hong Kong or take a train?
or连接的前后要一致,句前有will所以前面动词用的fly原型,后面必然要用take原形了.
who is the first person that eating cakes?
用eating,that后面是定语,-------谁是第一个人；应该是：谁是第一个吃蛋糕的人?而定语是修饰前面的,所以用ing.