Correct! The answer here is b.
This one is about keeping it simple. Why confuse things by saying what was "noticed" before instead of after the word "noticed"? Also, answer c is a more active approach to sentence writing. What is meant by active is that the objects follow the verb rather than the other way around. Note that answer d keeps the order right, but it is again much too wordy. A clear crisp sentence does not need those commas, which can cause a hurky-jerky reading. See below for some practice with active voice.