Answer:
The answer is B.
Unchecked emotions are potentially destructive.
Explanation:
He is comparing desire for love with fire which can be destructive and also ice with hate which can be just as destructive if not controlled.
A good explanation that I found about the theme of this poem states: "Frost equates fire with desire, a burning force that originates out of love and is equally destructive as ice, which he presents as similar to hate."(Theme of the poem fire and ice).