I'm ___ late for class. I always arrive on time.

The missing part of speech here is again an adverb of frequency. Since they always arrive on time and they are being contrasted with that, the missing word should mean the opposite of always, or some word which indicates they are not always late. The answer is "never", or an adverb that signifies not at all, or not usually. Given the options to choose from on the website, the answer is not directly visible, but it would be an adverb.