The number of people invited was fifty, but a number of them were absent for different reasons. 被邀请的人是五十个，但由许多人由于不同原因缺席了。
■“a lot of /lots of /plenty of /a large quantity of /a large amount of +名词”作主语，谓语动词的数与名词的数一致；如：
A large amount of damage was done in a very short time. 在短时间内造成了很大的损害。
A great amount of our investments are in property. 我们大量的钱都投资到房地产中。
但“(large /huge) quantities /amounts of名词”作主语，谓语动词一般用复数。如：
Large amounts of money were spent on the bridge. 那座桥耗费了大量金钱。
■“a +单数名词+and a half”和“one and a half +复数名词”做主语，谓语动词用单数形式。如：
One and a half pears has been left on the table. 盘子里剩下一个半梨子。