I'd say A is definitely the correct answer, but also C could be, if the Valley is a place, I really don't know if it is.
The subject of a sentence is always the topic or what the sentence is talking about / who is recieving the action. for example, "the dog went to take a walk." the subject is the dog. and the predicate is "went to take a walk" . once you identify your subject. you can find your predicate which is always the remaing part of the sentence or the action of the sentence.
Answer: 1) They are definitely playing music cards in the story.
2) I have sound knowledge that it is the game like solitaire games but I have never played this game.
Explanation: The clues that lead me to think that they're playing card games are; when Karen's friends arrived at her home, she collected the cards and then after deciding, they turned the music on.