Carbon dioxide from burning fuels is the most common of the so-called greenhouse gases.
I’m afraid this is the best way ____we can think of ____you.
All the universities have duty to _______ their students ____of the quick development of the scientific world.
I _______ spend the Saturday afternoon with my old friends in the zoo, but they did not come.
Reading books is very important for developing the students’ understanding of the world, ____?
Heating the news that my father was ill,I was so worried that I couldn’t on anything.