Statement 1: If Amisha works hard, then either Santosh or Ravi will enjoy themselves
Statement 2: If Santosh enjoys himself, then Amisha will not work hard
Statement 3: If Devika enjoys herself, then Ravi will not enjoy himself

Since Amisha works hard, either Santosh or Ravi will enjoys themselves, but if Santosh enjoys himself, Amisha will not work hard, this means Santosh cannot enjoy himself and it's Ravi who will have to enjoy himself whenever Amisha works hard. And since Ravi enjoys himself whenever Amisha works hard, Devika will not enjoy herself (from statement 3). Option D is correct.