The correct answer is B, inadequate.
The nymph says that IF we didn't grow old, and IF shepherd's always told the truth, THEN "these pretty pleasures might me move."
However, the promises made by the shepherd are inadequate. They will not say young forever and shepherd's do not always tell the truth. She needs more than the promise of flowers and songs. His offers are not enough to make her decide to go live with him and be his love.
She is not insulted by his words, but she realizes what he offers is not enough. She regards the shepherd's offer of love as inadequate. Therefore, the correct answer is B.