The correct option is B A promise can be broken without the person to whom the promise was made ever knowing.
The poem implies that making promises strips one of his/her liberty. As two persons might not ever know each other's past, so it's better not to make promises to each other. The last two lines of the first stanza also implies that the feelings of those who made successful and binding promises in the past can never be fully known. The line "Never false and never true/ let us hold the die uncast' implies that one cannot be judged faithful or unfaithful to a commitment that has not been promised. However, the poem never once states or implies that a promise can be broken without the person to whom a the promise was made ever knowing. So, option B is the best answer here.