30. Why was it hard to get rats images at night?
A. There was no enough light.
B. The rats moved very fast.
C. The rats were not big enough.
D. The cameras were in poor quality.
31. What will the study probably focus on in the future?
A. The effects of rats spit.
B. More advanced video cameras
C. The poison and rats' social behavior.
D. The relation between rats and poison.