Answer and Explanation:
An adverb is a word that modifies an adjective, a verb, or another adverb. Let's highlight the adverb(s) in each of the sentences given and then explain to which word they refer to.
a. Maurice and Laura shared meals regularly and enthusiastically.
In the sentence above we have two adverbs, "regularly" and "enthusiastically". Both are adverbs of manner, which means they indicate how an action occurs. They modify the verb (the action) of the sentence, "shared".
b. They often exchanged opinions and frequently agreed.
In the sentence above we have again two adverbs, "often" and "frequently". They are adverbs of time or frequency. "Often" refers to the verb "exchanged", while "frequently" refers to "agreed".
c. Later, Laura befriended Maurice's children, too.
Now we have one adverb of time, "later". It modifies the action "befriended", indicating the time when it happened.
d. Laura's book was very popular and deeply affected many readers.
Finally, we have two adverbs, "very" and "deeply". Both are adverbs of degree. "Very" is modifying the adjective "popular", while "deeply" modifies the verb "affected".