It is pretty well understood_______ controls the flow of carbon dioxide in and out the atmosphere today.

Whenever you enter the reading room, you can find all the students _____ at their desks, with their attention _____ on the books, except Tom [ ]

What’s the noise outside? —The kids ______ in the garden

gh you _________ find bargains in London, it’s not generally a cheap place to shop.

He sometimes goes to school_______ underground, but sometimes he _______ a bus.