Please keep _________ while I take yourphotograph

Working for the country，one must learn to ________ all his knowledge with the whole scientific world.[ ]

I don’t know why he ________ in the middle of a sentence.

If you just spend time__________advantages and disadvantages, you may get nothing in the end.[ ]

“Those sweet memories of summer days are about quiet streams and trees and shade.” The main structure of the sentence is .