Explanation:

The correct answer is option 'c' - "A merrier".

Comparative and Superlative Forms:
In English, adjectives can be used in different forms to compare two or more things. The comparative form is used to compare two things, while the superlative form is used to compare three or more things.

Formation of Comparative and Superlative:
The comparative form of an adjective is formed by adding -er to the end of the adjective. For example, 'merry' becomes 'merrier' in its comparative form.
The superlative form of an adjective is formed by adding -est to the end of the adjective. For example, 'merry' becomes 'merriest' in its superlative form.

Comparison in the Given Sentence:
In the given sentence, we are comparing the level of merriment during the holidays. The sentence states that "Everyone was home for the holidays". This implies that the level of merriment is already high because everyone is together.

To express a higher level of merriment, we need to use the comparative form of the adjective 'merry'. Therefore, the correct answer is "A merrier Christmas than that". This means that there is a possibility of a Christmas that is even more merry than the one described in the sentence.

Incorrect Options:
- Option 'a' - "A merryer" is not a correct word. The correct comparative form of 'merry' is 'merrier'.
- Option 'b' - "The merriest" is the superlative form of 'merry' and is not suitable in this context because it implies that there cannot be a Christmas that is even more merry.

Conclusion:
Based on the given sentence and the rules of forming comparative and superlative forms, the correct answer is option 'c' - "A merrier". This option expresses the possibility of a Christmas that is even more merry than the one described.

A merrier