根据句意和汉语注释，写出单词的正确形式。
As we know, oil always __________ (漂浮) on water.
He __________ (点头) to me in greeting when I entered the room.
We are very __________ (自豪) that a pupil from our school has won the prize.
They all hurried __________ (往楼上) to see what was going on.
There was __________ (沉默) for a moment and then someone made a useful suggestion.