How many times______ not to play with fire?-I’m sorry. I’ll never do that again.
Historically, __________main material for making tables has been wood, but__________metal and stone have also been used.
.______two articles to write today,I have to stay at the classroom to make it.
----_____is it that is troubling Mary ?----Working out the maths problem..
I wonder how long it will take you_____ such a hard task within so little time.
Tom was absent from school this morning, because sometimes he was a little weak and could ______ill .