Given below is a few situations, study them and state in which of the given cases work is said to be done. Give reason for your answer.
(a) A person pushing hard a huge rock but the rock does not move.
(b) A bullock pulling a cart up to 1 km on road.
(c) A girl pulling a trolley for about 2m distance.
(d) A person standing with a heavy bag on his head.