根据短文理解完成下列各题。

C

    Shenzhen is a city in South China. It is not very big, but it has attracted people of the whole country and the whole world as well.

    Just about twenty years ago, it was only a small fishing village. There were not many people there. Most of them lived on fishing. Things have greatly changed since the 1980's. It became the first special economic zone (经济特区) in China.

    Because of the opening policy(政策), economic changes between China and the outside world have increased greatly. People can come and go easily between Shenzhen and Hong Kong. Both foreigners and Chinese have built a lot of factories, companies and tourists' attractions there. People all over the country have come to find jobs. Many of them have settled down in this new booming(兴起的) city.

    Shenzhen is developing so fast that it has become a well-known metropolis(大都市) in China.

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癌了。

下图表示“制作洋葱鳞片叶表皮细胞临时装片”实验的部分操作步骤，步骤②和④滴加的液体分别是（   ）