题目

阅读理解Elephants might be the most well－known and well－loved animal in Africanwildlife. But conservation (保护) of the African elephantfaces special difficulties. While the elephant population is half of what itwas 40 years ago, some areas of Africa have more elephants than populated areascan support. That's why AWF scientists are studying elephant behavior,protecting habitats and finding ways for humans to live peacefully withelephants in Africa. Years ago, overhunting and the ivory trade were the biggestthreats to elephants' survival. Luckily, ivory bans (禁令), hunting rules an14．图中所示地区共同面临的生态问题是（　　）A．酸雨危害B．水土流失C．气候变暖D．土地荒漠化