Youcantakeanyseat____isfree.

-“You finally made it,didn't you ?”

-“ Yes， ____ your help,I wouldn't have succeeded.”

I still remember the days ____ we studied together.

The desk_____Tom is leaning is Jack's. It's covered with dictionaries.

Some concepts may be difficult to grasp chiefly because they may be unfamiliar or _____ideas, opinions which we already hold.