When you dont know the answer on a multiple choice questions it is generally best to

Go through the elimination process.

There are usually two answers that are wrong and that you can spot easily

Once you find the two wrong answers you are now left with a 50-50 chance rather than a 25% chance from the beginning.

Then I reread the question and see if it gives you any clues to what the answer would be in the multiple choice answer.

If you still cannot find an answer put something down because it is better to have something with the chance of getting it right rather than putting down nothing and getting it automatically incorrect.

Hope this helps! :3

answer; ron will have to compare ( b3: b4); /// good luck

answer; (c) series 3; i believe this is the correct answer. good luck