题目

下列各项属于旅游活动直接产生的环境问题是： ①台风过后，杭州西湖大堤上的树木被折断吹倒 ②修建黄山索道，砍掉山上林木48450立方米 ③在旅游风景区的许多景物上，经常见到“××到此一游” ④“水城”威尼斯因地基下沉，正遭受流水侵蚀和空气腐蚀 A.①②      B.②③       C.③④     D.①④According to a recent survey, _____ 90% of the students are interested in reading after class, they spend less time on it as they suffer increasing academic pressure.A.beforeB.whenC.whileD.unless