Only people with good logical thinking skills and a background in physics can be qualified for this position. If the above judgment is true, which of the following cannot be true? ['Zhao, a Ph. D. in physics, is qualified for this position.', 'Xiao Li, who has never studied physics, is qualified for this position.', 'Xiao Liu has a background in physics, but he is not qualified for this position.', 'Xiao Sun is not qualified for this position, but his logical thinking ability is recognized by everyone.']