Answer: A. He doesn't like it and refuses to drink it.
At the beginning of Part 2, we are told that Gregor wakes up to find a bowl of sweetened milk with pieces of bread that Grete has left for him. He is very happy to see it, as that is his favourite drink and he is starving. However, when he tastes it, he finds out he cannot stand the taste. He realizes that his physical transformation has also brought some inner changes, such as a change in the food he finds pleasant.