A)True.
In order to maintain relationships (both social and business relationships) a level of mutual kindness to each other is vital. Without kindness, a connection is impossible to be made. Additionally, if everyone was unkind, the world would be a much colder place than it is currently. Without kindness, compassion doesn't exist, which may result in social incompetence and increased wars and fighting.
The subjunctive mood is the best.
The subjunctive is rarely used in colloquial English. Totally irrelevant information, but... it is a relic from Latin, where there are many uses for a subjunctive. There is even a special conditional using the subjunctive mood that expresses the exact circumstances you described, which is usually called future less vivid.
I would say the answer is C
