Study
this situation:
សិក្សាស្ថានភាពនេះ៖ Read in English only
Yesterday, Dave and Susan
went to the park to do aerobics. They did it for an hour and they took a rest.
They both sat on a bench. Then Mr. Bob came to talk to them. Seeing a lot of
sweat on their body, he asked, “had you been doing exercise?” “Yes, we had been
doing aerobics for an hour before you arrived” they answered.