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."

如图，已知△ABC中，∠ABC=45°,AD⊥BC于点D，BE⊥AC于点E，F是AD和BE的交点，CD=4，则线段DF的长度为   

在一定条件下，在一个密闭容器内发生某反应，测得反应过程中各物质的质量如下表所示，下列说法错误的是（    ）