Mary is a humorous and warm­hearted woman and that is ________ she is a most popular person in her community.

-- Why do you walk so strangely? --- This is ______ I fell over myself accidently yesterday and my left leg got hurt.

The reason why they failed the test was ____ they didn’t sleep at all the night before. 

Xiao Ming practises his spoken English once there is a chance and that is_________ it takes to live his dream to be a good guide．

Action, not talk was       she graded her students on．