I think more than one ___ that half of the students___ here

I think more than one ___ that half of the students___ here from China
A.konws；are B：know are
I'd appreciate___ if you could turn the radio down.I‘m doing my homework.
A.you B that C this D it
It seems that the aged people ___ the H7N9 more easily from the recent cases.
A pick up B mix up C set up D use up
并说明理由