while, when, as; their them, the

while, when, as; their them, theirs People who hold higher position in a given group often overestimate their performance,_________ people in the lowest levels of the group underestimate __________.
【正确答案】：while, theirs
【题目解析】：第一个空格需要表示前后对照关系的关系词，只有while符合要求。第二个空需要一个名词性物主代词代替跟前文一样的内容 their performance。