This river has changed its course many times. It _________ always located where it ________ at present.

——Do you have any idea when the project will be carried out?—No, but I have heard that it was not until last month _______ it was approved.

It was soup _________ Oliver was eating.

Was it through Mary _____ was working at a high school ____ you got to know Tom?

I just don’t understand ______ that leads to so many teenagers becoming addicted to playing computer games.