were前边既然出现了there,那么也就是“there be”（有.....）句型了。last Sunday“上周日”说明是过去时，classes时复数，所以be动词应选were
was 过去时，因为是上个礼拜天。。有no ...用单数
werelast Sunday 上周日,用一般过去时, There was/ were.. classes是复数,所以用: were
因为要用过去时
