A plane is a machine that can fly.(指一类人或事,相当于a kind of)A plane is "a" machine that can fly.(指一类人或事,相当于a kind of) In many places in China,"the "bicycle is still a popular means of transportation.（表示某一类

A plane is a machine that can fly.(指一类人或事,相当于a kind of)A plane is "a" machine that can fly.(指一类人或事,相当于a kind of) In many places in China,"the "bicycle is still a popular means of transportation.（表示某一类
A plane is a machine that can fly.(指一类人或事,相当于a kind of)
A plane is "a" machine that can fly.(指一类人或事,相当于a kind of)
In many places in China,"the "bicycle is still a popular means of transportation.（
表示某一类人或物
）
这两句中 为什么第二句用“the”?不是也指一类物吗?

A plane is a machine that can fly.(指一类人或事,相当于a kind of)A plane is "a" machine that can fly.(指一类人或事,相当于a kind of) In many places in China,"the "bicycle is still a popular means of transportation.（表示某一类
第二句你的subjective(主语) 是Bicycle(自行车) 用The是特指bicycle 这个主语,表强调中国很多地方主语（自行车）仍然一种流行的交通工具　;而第一句 a用在句首泛指,如a man who from　US　一个来自美国的男人而我们很少说：the　man　who　from　US．　第一句就泛指飞机,但却并没有限定是哪架或哪种类型飞机波音或是阿帕奇等．