已知函数f（x）=3$\sqrt{4-x}$+4$\sqrt{x-3}$，则函数f（x）的最大值为（　　）

Li Ming is staying with the Wang's family for the weekend.
Today it is warm and fine. The family are having dinner in the garden. They often have dinner in the garden on a warm and fine spring day. Now Mr. and Mrs. Wang are sitting at the table with Li Ming under a tree.
"It's great to have dinner out here on such a lovely day," Mrs. Wang says. "What's the weather like in your hometown, Li Ming?"Mr. Wang asks. "It's not very warm in spring. But I like the spring there best." "Help yourself to some cakes, Li Ming," Mrs. Wang says. "Thanks," says Li Ming. "The cakes are very nice. I enjoy the dinner very much."