Which question should a reader ask to identify an author's purpose? why did the author write this text? what evidence does the author provide? what is the author's opinion on this topic? how effective is the evidence?

 The question that a reader should ask to identify an author's purpose is "Why did the author write this text?"  

 There are various reasons why a text is written and it becomes evident in the type of language and words used by the author; Usually, it is written for the following purposes:

Persuasion: The author intends to convince the reader on a certain statement. Information: An informative text is used as a source of knowledge about a topic. Explanation: Function as a tutorial which a reader can follow to reach an objective. Entertainment: Created for the amusement of the reader Description: In a descriptive text the author uses adjectives, forming a picture of the situation increasing the understanding and connection of the reader with the story or text.