Which sentence contains an error in the needn't-have versus didn't-need-to past-necessity contrast?
I carried the spare paddle all day but never used it, so I needn't have packed it.
The bridge had no toll, so we didn't need to buy a pass and bought none.
The hostel had many empty beds, so I needn't have reserved one even though I made no reservation.✓Правильный ответ
We cooked six portions and discarded three, so we needn't have prepared so much.
Объяснение
The sentence about the hostel is erroneous because needn't have reserved implies a completed reservation, yet the premise says none was made. Didn't need to reserve matches an unnecessary action that was not performed.