classroom is cleaner than

Have you found your lost dictionary?—-No,I haven’t found_____,but I bought _______this morning.

This is 3-D printer. And this is an artificial (人工的) ear. Can you believe that scientists printed this artificial ear by this 3-D printer?

Look! The students are playing on the playground. Some are running, some are playing basketball, ________ are watching.

Shanghai is the city ______ the 2010 world Expo is held. –So it is a city____ most of us want to vist this summer.