He is a person of sound character and ...... disposition.

In the sentence, "He is a person of sound character and ...... disposition," the word that fits appropriately to describe a positive disposition is:

Option C: amiable
The sentence would read: "He is a person of sound character and amiable disposition."

Here's a brief explanation of the other options:

Option A: beneficent means kind or charitable, but it may not be the best fit in the context of describing disposition.
Option B: morous is not a recognized word in English and does not fit the sentence.
Option D: amicable means friendly or peaceable, which is related to disposition but may not convey the same sense of amiability as "amiable."
So, the correct answer is Option C: amiable to describe a positive disposition.