a couple ofa glass of，det.几个;一对;

例句

I've come to crash on your floor for a couple of nights.

我来你家打几个晚上的地铺。

a glass of 一杯

例句

She stood up suddenly, upsetting a glass of wine.

她蓦然起身，碰倒了一杯酒。

a couple 表示一对，用于成对的事物，如，a couple of shoe 一双鞋，a glass of 是一玻璃杯，如：a glass of water 一杯水。