most of the stock reside (was damaged/damaged),but shocked workers(have been managed/managed)to save a small amount of it.
the police (are being investigated/are investigating)the cause of the fire,but it (is thought/thinks) that it was an accident.

Most of the stock reside (was damaged), but shocked workers (managed) to save a small amount of it. The police (are investigating) the cause of the fire, but it (is thought) that it was an accident.