Answer:
3. Least.
Explanation:
For making the sentence to be wholly meaningful and correct, the use of the right form of adverb according to the verb or words related is necessary. Adverbs are mostly used to modify the adjoining related verbs or adjectives. But they also help to intensify the manner or feeling or coure of action of the subject in the sentence.
based on the given sentence, The use of the word "least" in the sentence will intensify the action or feeling of the subject, here "the enemy". Thus, making the sentence into
The enemy was least worried about the knights than about the archers.
