Answer:
The correct answer is "With great sorrow and many fond memories"
Explanation:
The noun "sorrow" gives the phrase a formal tone because it is usually used in more ceremonial or polite situations and is not as common as the word "sadness".
At the same time, the adjective "fond" is more solemn than many of its synonyms, like "nice" or "dear", thus elevating the tone of the sentence.