I lost my friend’s bike, and I really don’t know ________.

Have you finished your homework ________? –Not ________. I was playing computer games.

The lady in this photo _______ be over fifty! She looks so young!

The soccer ball is 80 yuan .—I only have 50 yuan . I can’t _______ it .

He is one of the students who, I am sure, always do ____ best.