集体名词算复数。 for example, people are doing......
有些可数有些不可数网址http://wenku.baidu.com/link?url=Vvdf7CXF5aRQ91oU_l2bXslxLZ9NwMEbpMogr3Ul0CIY9-ghhbbM-1bNPcLMk03uhuYCBsdqeWdLTcKeRFA83knsmSMftuwbc91A9AoU7S7上面有
