plz explain, thx!

Waterloo Landscaping (WL) provided lawn and gardening services to homes and businesses in Kitchener-Waterloo. One morning while driving the WL truck to a client's home, a stray piece of gardening equipment ew out of the back of the pickup truck onto the highway. It smashed the windshield of the car behind it which caused that car to lose control which resulted in a crash involving another three vehicles. The driver of the WL vehicle had done the standard 'walk around' check of the vehicle before leaving that morning. Assume that due to the unique circumstances no insurance covers WL but they nonetheless get sued by all the vehicle owners. What legal claim would the vehicle owners make and what arguments would they make in relation to it? Is there anything WL could argue? (15 points)