Answer:
A. He is angry over an unresolved argument.
B. "I was angry with my foe: / I told it not, my wrath did grow."
Step-by-step explanation:
The poem "A Poison Tree" by William Blake revolves around the speaker's unresolved anger. The poem presents two cases where the speaker deals with the anger in him, and what happens if it is repressed.
Part A-
The cause of the speaker's wrath seems to be the unresolved anger he has against a foe which only makes him angrier. On the other hand, the anger he had with a friend was resolved after he let the friend know about it.
Part B-
The lines that support the argument that the speaker's wrath is caused by the unresolved anger are: "I was angry with my foe: / I told it not, my wrath did grow." This shows that the more he represses the anger he had for the foe, the more his anger grew. And the lines go on revealing that he 'cultivated' the anger into an evil weapon that 'killed' his foe.