18. For a social epidemic to occur, however, each person so affected must then influence his or her own acquaintances, who must in turn influence theirs, and so on; and just how many others pay attention to each of those people has little to do with the initial influential.

【分析】并列復合句。分號連接兩個分句。第一個分句的主干為 each person so affected must then influence his or her own acquaintances，后面 who 引導的定語從句修飾 acquaintances。 句中 For a social epidemic to occur 為狀語，so affected 是 each person 的后置定語。第二個分句中，疑問詞 how many 引導的句子作主語，謂語為 has little to do with，賓語為 initial influential。

【譯文】不過，要出現某個社會潮流，每個被這樣影響的人再去影響他們認識的人，如此循環下去。其他人中有多少注意到這些人，幾乎與最初的影響者沒有什么關系。

19. If people in the network just two degrees removed from the initial influential prove resistant, for example, the cascade of change won't propagate very far or affect many people.

【分析】句子主干為 the cascade of change won't propagate very far or affect many people。if 引導條件狀語從句，主語是 people，謂語是 prove， resistant 為表語，in the...influential 是 people 的后置定語。for example 為插入語。

【譯文】例如，如果在這個（相互影響的）網絡中，距離最初影響者僅有兩個級別遠的人就具有抵抗性，那么這一連串的變化就不會傳播太遠或影響太多人。

【點撥】1) removed 本句中用作形容詞“遠離的”，（be） removed from “遠離...的”。2) cascade 名詞意為“小瀑布；瀑布狀物；傾瀉”，動詞意為“傾瀉；大量垂懸”，本句中是要表達“一連串”的意思。3)propagate“繁衍；傳播；宣傳”，句中意為“傳播”。