The research mainly deals with the difficulty the students have ________ their attention on their study all the time. [ ]

The workers in the Huashan Mountainshave to rubbish to keep themountains clean.

Please be quiet. My little child_______.

been possible, I would have gone toattend Monica in the hospital, but Ifully occupied lastmonth.

Bill, is the pink umbrella Anna’s— No, it _____ be hers. Hers is purple.