Officials believe that more than one person _____ for the big fire.
.---There is a lot of smoke coming out of the teaching building.---Really? It _____be a fire, most probably.
–Did you find your new dictionary?---Yes. I found it ____I had left it.
–Will you ______me ____out this problem myself?---OK.
–When did the concert_____?---Oh, two days ago.
________arriving in Tibet , the soldiers at once joined them ____their work.At; with B. On; in C. For; with D. After; to