Simply put, a proposition is a declarative sentence. Others such as exclamatory sentences, interrogative sentences and imperative sentences are not propositions.

This is the most basic and not difficult to master. Work hard!

The above (1) is an exclamatory sentence, so it is not a proposition. (3) It is a question, not a problem. (4) It is an imperative sentence, not an imperative sentence. (6) It is an exclamatory sentence, not an exclamatory sentence. 13 is an expression, not a declarative sentence, andno. (17) is an imperative sentence, not a sentence.

In a word: (1) (3) (4) (6) (13) (17) is not a proposition. The rest are propositions.

One thing to note here is that the proposition is not necessarily right or wrong. As mentioned above, (12) is a wrong proposition.