I would go for A.
b) The toxins given to the rabbits in the two cages were of varying strength.
Doesn't help the conclusion.
c) Injecting the rabbits with toxins made them sick.
If so, then all the rabbits in both cages should have fallen sick.
d) Even without the exposure to cold temperature, the rabbits in the first cage would have probably gotten sick.
e) Even exposing rabbits to slight variances in temperature is likely to induce illness.
If so, all the rabbits in the first cage should have fallen sick.
a) The exposure to cold temperature acted as a catalyst for the toxins which made more rabbits in the first cage sick.
This seems to be the best answer.
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