题目

阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。Tourism can be both good and bad. Yes, it has brought in money for the local economy and(create) jobs for locals, but it has also brought some problems.One growing problem is tourists who want to provethey have visited a destination.Tourists have used paint, rocks, or even(key) to write on many places of interest. I have three words for people like this: please stop it. If you want to leave a mark on the world, do itchanging someone's life with kindness and love.Another big problem in some places 已知点O在二面角α－AB－β的棱上，点P在α内，且∠POB＝45°．若对于β内异于0的任意一点Q，都有∠POQ≥45°，则二面角α－AB－β的大小是________．