47 What is the main idea of the second paragraph?
(A) The meaning of the word endorphin shows its ability to take away our pain.
(B) When we have sex, do exercise, or eat food, our brain calls for endorphins.
(C) The word endorphin is formed by the two words endogenous and morphine.
(D) Endorphins stop sending pain signals by locking into special receptor cells.

我自己研究出的解題技巧（搭配下文）
①主旨=一切的基礎=根源性，其他句子以此為基礎延伸。
②也就是「其他句子以它為源頭/補充說明它」的句子就是主旨！
本題選項，BCD都是從A延伸出來的。
③再確認一下：A的重點：功用(BD說明)、以字表義(C說明)

One thing that is known for certain about endorphins isA）their ability to make us feel oh-so-good, or the so-called “endorphin rush.” We can see this in the formation of the word “endorphin.” C）說明該單字的組成It consists of two parts: endo-and -orphin； these are short forms of the words endogenous and morphine, intended to mean “a morphine-like substance originating from within the body.” B）在何種情況下作用When our body is subjected to certain stimuli like sex, exercise, food,or pain, our brain calls for endorphins, and the cells throughout our body that contain them answer the call. D）如何起作用When endorphins lock into special receptor cells, they block the transmission of pain signals and also produce a euphoric feeling—exactly like what morphine can do to us.