The difference between "some time" and "sometime" lies in their usage and meaning:

• Some time: This is a two-word phrase where "some" acts as an adjective describing "time." It refers to a certain period or span of time, often implying a long duration. For example, "It will take some time to finish the project."

• Sometime: This is a single word that functions as an adverb. It refers to an unspecified point in time, either in the past or future. For example, "Let's meet sometime next week."

Now, for the sentence "I saw him again........last week," the correct answer is D. sometime. The phrase "sometime" fits best because it indicates an unspecified period during the last week.