Answer:
The correct answer is B.
Step-by-step explanation:
Answer B is an example of stage directions because in the phrase "A messy bedroom. CHRIS sits back on the bed strumming a guitar." express that Chris sat down (gives an address, sitting) on the bed (a stage, which in this case is the bed). And besides, it may be that the words "a messy bedroom" give a space indicator (scenario) as well.