The correct answer is: D. Neither I nor II follows.
The first statement is “Irregularity is a cause for failure in exams.” This means that if a student is irregular, they are more likely to fail. However, it does not mean that all irregular students will fail, or that all regular students will pass.
The second statement is “Some regular students fail in the examinations.” This means that there are some students who are regular and still fail. This does not contradict the first statement, because it is possible for a student to be regular and still fail.
Conclusion I is “All failed students are regular.” This is not a valid conclusion, because the first statement does not say that all irregular students will fail.
Conclusion II is “All successful students are not regular.” This is also not a valid conclusion, because the first statement does not say that all regular students will pass.
Therefore, neither conclusion I nor II follows.