a和the的用法a pen和the pen的区别在哪里呢?难道说起一件东西的时候 必须在前面加上a或者the么?各位大神

i has bought a pen 和 i bought a pen 的区别 The little boy needs a blue pen 里的表语? Whose pen is this 和Whose is this pen的区别在哪里 There is a pen and an eraser in the box否定句和一般疑问句和a pen and a 定语和状语的区别例如the boy here needs a pen中的here为什么是副词作定语而不是地点状语,什么情 There have a pen on the desk.哪里错了 the+序数词和a+序数词的用法区别 Give me that pen._____ on the desk.A:The red pen B:A red pen 1.I have a pen pal in the United States和I have a pen pal fro that is a pen /that is the pen有什么区别? The boy in the classroom needs a pen of yours的定语是什么? 这里的冠词a和the用法