C.) It emphasizes that the narrator is having trouble making her limbs obey her. This is the right version.
The narrator's limbs have got "slow" because she has got really tired. She is trying to climb up a mountain. She feels this state mainly through her arms and legs. These cannot move in spite of her will power; she wants them to move but they do not respond. Therefore, the personification: "my arms and legs have gotten the message yet ......" and "....come on now, arms: one......, start climbing!" seem to indicate her limbs have their own volition.
These options are not right:
A.) It demonstrates that the story is only a fantasy occurring in the narrator's mind. ( It is not a fantasy; she is truly climbing up a mountain).
-B.) It suggests that living things are more complex than they appear to be. ( The writer is not reflecting upon any issue; she is just narrating events).
D.)It reveals that the narrator has superstitious ideas about the human body.( She is just expressing her real feelings with personifications).