a number of +名词复数,"许多,一些",作主语时,谓动用复数.
plenty of +可名复,"大量的,足够的" ,作主语时,谓动用复数.
plenty of +不可名,"大量的,足够的" ,作主语时,谓动用单三
如:A number of new products have been successfully trial - produced.
许多新产品已试制成功.
Plenty of money often fetches out a person's worst qualities.
面对大量的金钱往往会使人暴露出最坏的品质.
Plenty of foreign firms have set up factories here.很多外国公司已在这里开办工厂.