The least possible Venn diagram for the given statements is as follow,
Conclusion: I. Some cats are mice → True (It is clear from the Venn diagram as "Some cats are rats and all rats are mice" so some cats are mice, it is definitely true) II. Some mice are cats → True (It is clear from the Venn diagram as "All rats are mice and some cats are rats" so the some mice are cats, it is definitely true) Hence, "Both conclusions I and II follow" is the correct answer.