Hello. You did not inform the section to which this question refers, which makes it impossible for this question to be answered. However, I will try to help you in the best possible way.
First, it is important that the theme, or the central idea, of a text is the main subject being discussed in the text. This is the subject that will be developed and worked on throughout the text.
In that case, to answer your question, you will need to read the entire passage and recognize the subject being exposed in that passage. This subject will not be explicitly mentioned in the passage, but you will be able to recognize it if you analyze the situation that the passage is presented. For example, if you read a text that shows the characters starving, without money to feed themselves and without being able to have a safe home. This passage may present themes such as poverty, income imbalance and social problems. Similarly, if you read a passage where the character is taking revenge on someone, but feels unhappy, you can see that the text has the theme that evil will always result in unhappiness.
