a fifth column

organized group of people working for the enemy within a country at war 第五纵队（战时在国内为敌人工作的组织）.

a, a (large) number of, a bill of fare, a bit, a case in point, a couple of, a far cry, a few, a fortiori, a gentleman's agreement, a good deal, a good few, a good many, a great deal, a great deal of, a great many, a great/good deal of, a hard nut to crack, a kind of, a la carte, a la mode, A level, a little, a lot of, a matter of, a mite, a mountain of, a number of,