__________ he is old, the old man still insists on studying at a night school.

 In the office an electrical engineer is looking through the instructions to know ________ the heat system works before the repair work.

Work hard when young, ______ you will regret.

In the US, students can do almost anything they want in class, ____ they don’t make too much noise or disturb others who want to learn from the teacher. 

I made a promise to myself _______ this year, my first year in high school, would be different.