题目

    A lot of teachers hate doodlers(乱写乱画的人)during classes. “Pay attention!”Teachers will often warn doodling students，sure that they must be daydreaming.     However, according to a recent study, doodling while listening to a boring lecture helps  concentrate the attention：        Andrade，a psychology professor in England asked participants to listen to a boring lecture.  Half the participants were told to color in squares and circles freely on a piece of paper while listening to the lecture. The other half weren’t given a task. After it was over, the part 已知点P(x，y)在经过A(3，0)，B(1，1)两点的直线上，那么2x＋4y的最小值是 [　　] A． 2 B． 16 C． 4 D． 不存在