Answer:
B. The final couplet reverses the ideas of the three quatrains.
Step-by-step explanation:
Just look at some examples:
"Yet him for this my love no whit disdaineth;
Suns of the world may stain when heaven's sun staineth." (Sonnet 33)
"But thou art all my art, and dost advance
As high as learning, my rude ignorance." (Sonnet 78)
" But thence I learn and find the lesson true,
Drugs poison him that so fell sick of you." (Sonnet 118)
As is seen in these couplets, they reverse the ideas of their sonnets. The conjunctions yet and but are used to introduce a phrase or clause contrasting with what has already been said.