Omg i remember reading this story! A fav!
Ok so:
Four sound are
planes bombing (unpleasant)
Marching of the nazis (unpleasant)
Children playing (pleasant)
Music? I forgot what the instrument was but they heard an instrument (pleasant)
The answer is: figure out meaning based on what you already know and what the text says
To infer something from the passage, you need to read it and able to understand the meaning of the passage without actually put too much focus on the passage.
Passage inference could be considered as a reading skills. This usually tested when you do an SAT test to measure how much information you can gather from reading a certain text within a short period of time.
The correct answer should be locate basic information.
When you are doing the preliminary research, you are just reading through a bunch of sources and information that you may or may not use while writing. You still aren't deciding which exact sources you are actually going to use, but rather just trying to find them and later on make that decision during another stage of writing.