Answer:
To determine the word that comes last in alphabetical order, we need to arrange the given words in alphabetical order and then identify the word that appears last in the list.

The given words are:
a) Warring
b) Waving
c) Watching
d) Waiting

Arranging the words in alphabetical order:
1) Warring
2) Waving
3) Watching
4) Waiting

Identifying the word that comes last:
To identify the word that comes last, we compare the words in alphabetical order letter by letter from left to right.

Comparing the words:
1) Warring vs Waving
- The first letters are the same ('W' vs 'W'), so we move to the next letter.
- The second letters are the same ('a' vs 'a'), so we move to the next letter.
- The third letters are different ('r' vs 'v'). Since 'r' comes before 'v' in the alphabetical order, 'Warring' comes before 'Waving'.

2) Warring vs Watching
- The first letters are the same ('W' vs 'W'), so we move to the next letter.
- The second letters are the same ('a' vs 'a'), so we move to the next letter.
- The third letters are different ('r' vs 't'). Since 'r' comes before 't' in the alphabetical order, 'Warring' comes before 'Watching'.

3) Warring vs Waiting
- The first letters are the same ('W' vs 'W'), so we move to the next letter.
- The second letters are the same ('a' vs 'a'), so we move to the next letter.
- The third letters are different ('r' vs 'i'). Since 'r' comes before 'i' in the alphabetical order, 'Warring' comes before 'Waiting'.

From the above comparisons, we can see that 'Warring' comes before all the other words. Therefore, the word that comes last in alphabetical order is 'Waving' (option B).