It is repoted that the museum had been broken into and a lot

It is repoted that the museum had been broken into and a lot of things ____________.A.stealin...
It is repoted that the museum had been broken into and a lot of things ____________.
A.stealing B.were stolen C.stolen D.had been stolen
答案给出的是B,不知为何,请高手指教.
错了，答案给出的是C，我自己选的是B