If_____litters, our world will be more beautiful.
The number of students in our school_________ more than 2000.
At the science museum,the boys and girls get to know__________.
The more you smile, the ___________ you will feel.
We should study the new traffic rules and 1earn how___________ ourselves.
--- Does Ted tell you if he _______________ next Sunday?--- No, he does’t. But if he ________________, I’ll give you a ring.