House owns his home in City. On the lawn in front of his home and within five feet of the public sidewalk there was a large tree. The roots of the tree caused the sidewalk to buckle severely and become dangerous. An ordinance of City requires adjacent landowners to keep sidewalks in safe condition. House engaged Contractor to repair the sidewalk, leaving it to Contractor to decide how the repair should be made. Contractor dug up the sidewalk, cut back the roots of the tree, and laid a new sidewalk. Two days after House had paid Contractor the agreed price of the repair, the tree fell over onto the street and damaged a parked car belonging to Driver. Driver has asserted claims against House and Contractor, and both defendants admit that cutting the roots caused the tree to fall.The theory on which Driver is most likely to prevail against House is that House is
strictly liable, because the tree was on his property.  liable for Contractor's negligence if, to House's knowledge, Contractor was engaged in hazardous activity.  liable, because he assumed responsibility when he paid Contractor for the repair.  liable on the basis of respondeat superior