Correct Answer: more

Solution : The correct choice is the first option.

• More is the most appropriate option in this context. It implies a greater quantity or extent, suggesting that the speaker regrets not being able to spend a greater amount of time with the person over the summer.
• Many and much are used to quantify countable and uncountable nouns, respectively, but they are not suitable in this context because the focus is on the extent or duration of time spent with the person.
• Many more is not incorrect, but in this sentence, "more" alone is sufficient and sounds more natural. The use of "many more" might be appropriate in a different context where a specific countable quantity is emphasised.

Therefore, the complete sentence would be: "I am sorry that I was unable to see more of you over the summer."