A number of birdwatchers ______in Zhalong Nature Reserve. The number of them____500.

“________ do you exercise?” “Three times a week. ”

I simply couldn’t understand how it _____ that you did so much work within such a short time．

I met Daniel in the street yesterday, I ________ him since he left for Beijing.— Well, does he look like what he used to be?

I called you yesterday evening, but nobody answered the phone. –Oh, I ___ a walk with my parents at that time.