填入下面一段文字横线处的语句，最恰当的一句是 （ ）辣，我们都不陌生，很多人无辣不欢甚至吃辣上瘾。这是因为辣椒素等辣味物质刺激舌头、口腔的神经末梢时，会在大脑中形成类似灼烧的感觉，机体就反射性地出现心跳加速、唾液及汗液分泌增多等现象， ，内啡肽又促进多巴胺的分泌，多巴胺能在短时间内令人高度兴奋，带来“辣椒素快感”，慢慢地我们吃辣就上瘾了。

13．About 90 percent of the equipment presented by the administration，as well as the facilities ofour own，______made good use of in teaching．

The number of the books in our school library _______ about50,000.

14. Over the long process of evolution, animals have developed their ______ senses, which makes it possible for them to _____ their environments.

Some naughty boys like to play ________ trick on their classmates on April Fool’s Day.