For flowchart questions, we usually will start from the top and work our way down so as you hit each property think about whether it’s suitable for making a screen protector

Is it fragile? No we do not want a fragile protector as we need it to protect the phone.

Is it flexible? Screen protectors tend to be flexible and thin so yes we want it to be flexible

Is it waterproof? Yes we need it to be water proof to protect the phone.

So we want material D as it is not fragile, but it’s flexible and waterproof.

Understand the properties you need in your material and just follow the flowchart and you should be able to answer this :)