在△ABC中，D为BC中点，DE⊥AB于E，DF⊥AC于F，已知DE=DF，则下列结论不一定成立的是（　　）

    As prices and building costs keep rising, the “do-it-yourself” (DIY) is getting more and more popular in the USA.
 “We needed furniture for our living room,”says John Rose,”and we just didn't have enough money to buy it. So we decided to try making a few tables and chairs.”John got married six months ago, and like many young people these days, they are struggling to make a home at a time when the cost of living is very high. The Roses took a 2-week courses for ＄280 at a night school. Now they build all their furniture and make repairs around the house.
    Jim Hatfield has three boys and his wife died. He has much work at home as well as a job in a shoe-making factory. Last month, he received a car repair bill for＄420. "I was deeply unhappy about it. Now I've finished a car repair course, I should be able to fix the car by myself.”
John and Jim are not unusual people. Most families in the country are doing everything they can do to save money so they can fight the high cost of living. If you want to become a DIY, you can go to DIY classes. And for those who didn't have time to take a course, there are books that tell you how you can do things yourself.