5.Since the 1930s, hundreds of stone balls have been found in Costa Rica. It's believed that they ______ by the ancestors of native people who lived there at the time of the Spanish conquest.
答案是could have been made，知道是被動式，但是不了解為何要用could+完成式，是要跟前面句子時態一致嗎?
用過去完成式，表示比過去式早，因為ancestors是建balls的人，他們比以前住在那裡的native people的時間更早。
6.More and more parents find _____ a headache to regulate the time their children spent on the Internet.
答案是it，我選that。仔細看這裡應該不能放名詞子句的連接詞that，但是find it a headache to...，感覺怪怪的，是不是省略掉什麼字了呢?
這裡的it是虛受詞，代替後面的延遲受詞to regulate the time their children spent on the Internet.
a headache是受詞補語。
7.Nowadays, as new technologies, such as mobile phone Internet access, evolove, _______.
(1)so does the work of the cybercriminals
(2)the work of the cybercriminals as well
(3)the work of the cybercriminals, too
(4)so the work of the cybercriminals does
答案是(1)，這題答案看完我就神遊了，這題要怎麼翻譯呢?
as ..., so ...是這句的關係：隨著新科技的進步，網路犯罪也進步了。
手機上網只是為新科技舉一個例而己。
