please help me to answer this qution

III/ Add articles where necessary. a) A dog that bites should be kept on leash. b) He gave me CD's he liked best. c) The classroom contained a blackboard, eraser, and computer. IV/ Correct the sentences so there are no tense shifts. a) The teacher entered the room and then roll is called. b) The wind was blowing hard when there is a big crash. c) The prisoner told the parole board that he promises to stay out of trouble. d) Medical researchers know that asbestos caused cancer