There are only one thing you can do: to tell the truth.

1.不定式作one thing的同位语？也就是说冒号可以引出与其分隔开来的前面某个词或词组的同位语？

语法书中冒号相关内容：

The functions of the colon, a rather infrequent punctuation mark, can be summed up as follows: what follows (as in this sentence) is an explication of what precedes it or a fulfillment of the expectation raised (even if raised only by its own use). Thus:

I've just had some good news: I've been offered a job in a law firm.        [1]

Those who lead must be considerate: those who follow must be responsive. [2]

In [l] the explication is a clause which can be viewed as being in apposition to a noun phrase in the preceding clause, if the notion of apposition is extended beyond noun phrases (cf 17.65 ff). Compare:

The good news is that I've been offered a job in a law firm. Such a relationship is typical between units separated by a colon. A further example：

The man has been drinking heavily：this，not age，explained his unsteady walk.[3]

Here the pronoun this refers back to the whole of the preceding clause ('the fact that the man had been drinking heavily'). Sometimes the relationship is more indirect and subtle, however, as in:

Joan and Mary were obviously weary: I got up to go.  [4]

The colon in [4] helps to indicate that it was my observation of their weariness that made me decide to go.

2.语法书这里意思是冒号可以引出对前面整个句子或某个部分的解释说明成分然后后面那个不懂是啥意思，并不一定是同位语吧?

3.那么不能分析为同位语时，应当把冒号后视为解释说明前面一句话的分句或短语吗？

4.例句3、4冒号前后并没有表示同位关系，只是对前面句子的解释说明？Here the pronoun this refers back to the whole of the preceding clause ('the fact that the man had been drinking heavily'). 这句话单纯解释this所表达的含义还是说指出冒号前后的关系，this是前面一句话的同位语？