This passage speaks mostly about Banquo's astute understanding of how the agents of evil work: they tell the truth about things that don't matter. Then they betray us in things that really do matter.
Which answer is closest to that interpretation? It certainly isn't B. There is no mention of Banquo's children. Nor of his children becoming kings.
C is possible. But there is no mention of Duncan at all. He says nothing about how Macbeth will go beyond being Thane of Cawdor. Just that there is something beyond the Thane of Cawdor.
D is not in support of murdering Duncan to get the throne. Banquo never was in favor of killing Duncan and he won't be when Macbeth does the grisly deed.
That leaves A. The remark I put at the beginning says just about what Banquo says in the passage.
