After walking on the zigzag path to the mountain top for a few hours, the tourists gathered under trees_____ shade and______ down to have a rest.

When the teacher came in, the students pretended _____ the text.

Have you heard of it? Firefighters rushed into a burning house, three of them unfortunately _______ in and ________ their lives.

Some very common things such as    to the sun for a long time will do harm to people's skin and even cause skin cancer

Do tell me the way you think of ______ the problem as soon as possible.