Which of the following words has its letters in alphabetical order?

Let's analyze the alphabetical order of the letters in each word:
* Behind $\to$ B, E, H, I, N, D (D comes after N, so not in order)
* Below $\to$ B, E, L, O, W (Positions: B=2, E=5, L=12, O=15, W=23. This is strictly in increasing alphabetical order)
* Beside $\to$ B, E, S, I, D, E (not in order)
* Between $\to$ B, E, T, W, E, E, N (not in order)