One reason why section 4 is difficult is that you might hear the answer to a question before you hear the 'keywords' from the question. Here's an example to show you what I mean:
Question (from Cambridge IELTS 7):
Undiscovered material may be damaged by ______.
When listening to the recording, you are waiting to hear the keywords "undiscovered material" and "damaged by", and you are hoping to hear the answer after hearing those keywords.
This is what you hear:
Don't make fires, however romantic it may seem. It's really dangerous in dry areas, and you can easily burn priceless undiscovered material by doing so.
Can you see that the answer came before the keywords "undiscovered material"? What is the correct answer?
There isn't a special technique to help you with this type of question; you just need to be aware that you might have heard the answer before you hear the 'keywords'.