Concept: The opposite of the word "hostility" is a term that describes friendliness or peaceful relations.
Explanation: Hostility means unfriendly behaviour, opposition, or enmity toward others.
The word that best opposes this idea is "amity", which means friendly and harmonious relations.
"Happiness" refers to a feeling of joy, not a relationship between people.
"Agreement" means having the same opinion, but it does not directly oppose hostility.
"Freedom" means independence, which is unrelated to friendliness or opposition.
Therefore, "amity" is both the nearest opposite and the correct word to fill the gap.
Answer: B. amity.