Sundays后面为什么要加S?

Sundays后面为什么要加S? I never get up early on Sundays.为什么Sunday后面要加s You visit yourgrandmother on Sundays. Sundays这里的“s”为什么要加,如果不加“s”,这句话对吗? They don’t work on Saturdays and Sundays.为什么用don’t来否定Saturdays和Sundays后面为什么加s? She often does some shopping on sundays.这句话该怎么翻She often does some shopping on sundays.这句话该怎么翻译?还有后面sunday为什么要加s? She often does some shopping on sundays.这句话该怎么翻She often does some shopping on sundays.这句话该怎么翻译?还有后面sunday为什么要加s? We stay at home on Sundays这句话最后的Sunday要大写么?为什么?还有sunday后面用不用加S My grandfather often goes fishing on Sundays.(爷爷经常在星期天去钓鱼.) 为什么Sundays要加s hobie s后面为什么要加s? we don't have classes on sundays.中的sunday为什么要加s' i often go shopping on sundays .为什么sanday要加s啊 She never goes out on Sundays句中,sunday为什么要加s? 为什么play后面要加s 为什么any other后面要加s? 有些动词后面为什么要加s? 为什么有些like后面要加s minutes'后面为什么要加s' 为什么make后面要加 s