in a dictionary,all the words(beginning)with "a"come first,then those(beginning)with"c"and so on

题目

in a dictionary,all the words(beginning)with "a"come first,then those(beginning)with"c"and so on
为什么用动名词?表示什么.

答案

动词ing形式作后置定语修饰名词或代词,相当于形容词.beginning“以...开始的”