The correct option is D he heard the loud barking of the wild dogs
Option C: According to the lines "One day Bunny Rabbit heard the loud barking of the wild dogs. He was very scared.", the rabbit got scared because of 'he heard the loud barking of the wild dogs'.
Hence, option C is correct.
Option A: This line is neither mentioned in nor implied by the passage.
In fact, he has a lot of friends: "Poor Bunny went to the monkey, elephant, goat and all his friends."
Option B: The bunny's home isn't mentioned in the passage at all. So, this cannot be the reason for his fear.
Option D: Similarly, a lion also isn't mentioned.
Hence options A, B and D are incorrect.