问题补充：
上海高考英语完形填空The photo attached to the application was sometimes that of a very good-looking person and sometimes that of a less attractive person. 这两个that 是怎么回事？
答案：
【答案】 was是系动词，系动词后面跟的是表语或表语从句，而此句中of是介词，与后面的构成介宾短语，介宾短语可以充当表语，而句中that指代photo，在句子中不可以省略！
