We were given an activity with this question yesterday and I’m not sure if my answer was correct since it seems like it works either way…
In this case, the word describes how someone looked at me. As it describes a verb, the word you need should be an adverb. Coldly is the adverb, so it is correct. In other cases, you can tell the correct answer by looking at the ending of the word. Adverbs almost always end in “ly”.
