题目

阅读理解The 30 by 30 campaign to protect 30% of the world'soceans by 2030, supported by more than 70 nations, is known mostly for ambitionand few achievements so far. Just 7% of the seas are protected and only 2.7%are highly protected.Setting aside nearly a third of the oceans, the fishers say, is anidea developing nations in South America and elsewhere can hardly afford. Thatargument against a large expansion of sea protected areas is heard around theworld, and the gap between conservationists and fishers has grown wider as fishpopulation declines and the appetite for seafood grows along △ABC中，D是BC的中点，E、F分别是AB、AC边上两点，且ED⊥FD，你能说明BE+CF>EF的道理吗？