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。

I don’t know________made Gong Li become an outstanding superstar at home and abroad.

Scientists say it may be five years ______ it is possible to test this medicine on human patients

The doctor told me to eat more ________ because it’s good for my health.

Would you mind helping me with my suitcase? I really can’t manage it by myself—– ________