a mass of后面加不可数名词单数,可数名词复数：a mass of earth一大块泥土 a mass of detail 大量细节,a mass of spectators大量观众,I got masses of cards on my birthday.我生日收到大量贺卡 I have masses of work/ things to do.A mass of snow and rock broke away and fell on the climbers.
manner方式,复数加-s
manners表示礼貌,规矩,一般就用复数形式,不用单数