德国小菊花官网:I found playing football frustrating.为什么 frustrating前不用加is?

I found playing football frustrating.为什么 frustrating前不用加is? i go on foot 中 on foot 是什莫短语 I found no stunts there I found I really need You I found I really need You I so thanked I found you I am so thanked I found you I often go ?.?处是填by foot,by walk,on feet还是on foot? I LIKING PLAYING THE PIANO！这句话对吗 I am fond of you and playing football.