I don't know who invented the machine,but I think it is a/the useful invention.a还是the?

来源：学生作业帮助网编辑：作业帮时间：2024/04/16 15:07:35

I don't know who invented the machine,but I think it is a/the useful invention.a还是the?
I don't know who invented the machine,but I think it is a/the useful invention.a还是the?

I don't know who invented the machine,but I think it is a/the useful invention.a还是the?
a 意为“一种”,表示泛指.