a number of 表示很多,大量,后跟可数名词的复数形式,be动词也用复数形式.
近义词有：many , a lot of , lot's of , plenty of , a quantity of , a good many , a great many , few , a mass of, masses of , a large quantity of .
下面是我总结的表示“许多、大量”的词或短语：
修饰可数名词的词或词组如：a good many,
a number of , many , few
修饰不可数名词的有： a great deal of,
a large amount of , much , little
即修饰可数又修饰不可数的有：plenty of, some,
any , a lot of , lots of , a mass of,
masses of , a large quantity of ,
quantities of
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