, the classroom is so dirty Itneeds ______ before we begin our class

People on the grassland ofisnow Kazakstan were the first to achieve both riding and milking horses

there are some differences in American education and Chinese education, bothsystems are excellent graduates.

The forest guards often find campfires that have not been _____ completely.

Hawking believes the earth is unlikely to be the only planet _____ life has developed gradually.