Some people say that watching TV will affect the learning of elementary school students, but a survey of a school found that students who watched TV at a school for a longer period of time performed better than students who watched it for a short time. It affects pupils' learning. Which of the following, if true, would most weaken the above inference? ['They surveyed school is not very representative.', 'Watching TV can broaden the horizons of primary school students, increase their knowledge, and help learn.', 'Parents of primary school students at the school let their children watch some educational TV programs.', 'Parents of elementary school children are allowed to watch TV only when their children have achieved good grades.']