Question

it is /this is 的分别??

Answer 1

The words this
that
these and those are demonstratives. In spoken and written English
demonstratives are generally used to ‘point to’ something in a situation. The demonstrative pronouns this and these usually refer to something which is near to the speaker
and that and those refer to something further away
e.g.: A: Do you like this scarf? It matches my coat. It is a pronoun and refers to those not human in nature. It may be in a picture or your thing. So
the thing may not near to you. I meet a cat when I e here. It is a black and white in color.
参考: onestopenglish/Grammar/Reference/Pronouns/demonstratives1
简单答： 当场眼见到或指得到出来的用this， 不是说现在发生的东西，不能在当场见到或指出的便用it。
前提: This is a pan ->This is a pen 以下用此作解释 It is a pen. it是指死物的代名词
只要是死物
要标示它就可以用it This is a pen. this有指方向的用途
通常指较近的
伸手可及的东西
和that相反 两者的分别
it是一般的陈述
但this有强调支笔比较近的意思 可能的情况是
有个谜语的谜底是一支笔
问你谜语的谜底是什么
只能答 It is a pen. 答This is a pen.一定错
因为没有一支实际的笔出现了