为什么on weekends要加s?

on weekends 为什么要加s 为什么on weekends要加s? what do you usually do on weekends 为什么加s he like goes to see Beijing Opera on weekends为什么要加s I often go to shopping on weekends在“I often go to shopping on weekends.”中week要不要加s的?为什么?请详细说明. do you go to the movies with your parents on the weekends?为什么movie要加S 为什么have a nice weekend!与on weekends的weekend 一个加s一个不加s? Lingling often goes swimming on weekends 为什么swim要加ing?这句话是什么时态? Do you think everyone enjoys their weekends?为什么enjoy要加s,不是一般疑问句吗? what do you usually do on weekends 为什么加s 是一般现实时吗不是三单才加s吗 问什么这里也加? weekend什么时候要加介词?我好像看到过this weekend,on weekends,at weekends on weekends 为什么要放在句子的最后 英语：at weekends为什么不用on weekends?详细! He sometimes go( )swimming on weekends,这句里的go要加s/es吗?过几天要期末考,别搞错了啊! on weekends,students should help their parents do some cieaning at home.clean为什么加ing为什么加ing do you think everyone enjoys their weekends 中enjoys为什么加s Do you think ereryone enjoys their weekends为什么enjoy加s on weekends 在周末为什么用复数