Additional social stress may also occur because of the population explosion or problems arising from mass migration movements--themselves made relatively easy nowadays by modern means of transport.
【解析】
從結構來看,該句because of 的后邊接兩個名詞短語the population explosion和problems arising from mass migration movements--themselves made relatively easy nowadays by modern means of transport來表示原因。其中,第二個名詞短語又含有一個短語themselves made relatively easy nowadays by modern means of transport,來補充說明mass migration movements。因此,這里的代詞themselves 指代名詞短語mass migration movements。
While there are almost as many definitions of history as there are historians, modern practice most closely conforms to one that sees history as the attempt to recreate and explain the significant events of the past.
【解析】
不定代詞one 指代名詞短語definition of history。在這里one 和物主代詞及人稱代詞在指代名詞方面有所不同, one 指代上文出現的名詞的同類名詞,其中,one 表示單數,ones表示復數;而物主代詞及人稱代詞必須指代上文中出現的名詞本身,所以單復數必須一致。比如這里若要用人稱代詞,則必須用 they/them來指代上文中復數形式的definitions of history。