A diagram is a way of tracking your information all together and a illustration is a picture of anything like a picture in a book
The answer should be "slow" the first pairing both end in "-est" making them superlatives giving a parallel in the structure. Following the same structure, the words from the pairing after can be ignored, the word dim is an adjective, "light" bulb is a noun, therefore, it is not a parallel structure.
They are prideful ....hope this is the answer
