3 a cup of; a glass of; a mug of

● 以上词组介词因cup, glass和mug的意义区别，一般不可互换。

● a cup of中的cup指有柄瓷杯，多用来装茶、咖啡等热饮料，如：Would you like a cup of tea?（你想喝杯茶吗？）Ordering a cup of tea, I struck up a conversation with the manager.（我要了一杯茶，便和经理攀谈起来。）

I used to have a cup of coffee after I got up in the morning.（我过去习惯早上起床后喝一杯咖啡。）Add two cups of sifted flour to one cup of sugar and mix.（把两杯筛过的面粉加到一杯糖里后拌匀。）

● a glass of中的glass指玻璃杯，多用来盛水、牛奶、酒等冷饮料。如：Please give me a glass of lemon tea.（请给我杯柠檬茶。）We had a pleasant chat over a glass of milk。（我们边喝牛奶，一边愉快地聊天。）He felt so thirsty that he had two glasses of water at a time.（他太渴了，一次喝了两杯水。）She likes to have a glass of beer before dinner.（她喜欢在饭前喝杯啤酒。）

● a mug of中的mug指有柄的大瓷杯或金属杯，强调“一大杯”，可装各种饮料。如： Can I have a mug of water?I’m terribly thirsty.（我能喝一大缸子水吗？我实在是渴极了。）He asked me for a meal and a mug of beer.（他向我要了一份饭和一大杯啤酒。）He carried a large slice of bread and meat and a mug of beer into a corner and applied himself to disposing of them with great voracity.（他拿了一大块面包夹肉和一大杯啤酒，躲到一个角落里狼吞虎咽地吃起来。）Make a mug of coffee for me, please.（请给我煮一大杯咖啡。）She felt much better after drinking a mug of cold water.（喝了一大杯凉水之后，她觉得好多了。）