都可以做主、宾、定、状、补语
主语：
To finish the work in such a short time is not easy.
Learning English is not easy.
宾语：
I want to swim in this pool.
I like dancing.
定语：
That was the first thing to do.
That was a flying machine.
状语：
To improve your oral Enlgish, you must have more practice.
Standing at the top of the mountain, you can see everything along the river.
补语：
Do you me to go there?
I saw him entering the room.