The love that we call "friendship" is different than erotic love because, while erotic love can be fully present even if the other person doesn't love me back, true friendship aims at love.

mutual

Explanation:

Mutual love simply put is the type of love relationship that goes both ways. It entails that both or all parties involved love the other party equally. Mutually love is mostly expressed in true friendship.

It is entirely different from erotic love. Where erotic love is one sided and not returned by one party in most cases, mutual friendship ensures both parties love each other back.

b) to encourage free trade

it would be d). more resources must be obtained to attain that combination of goods and services