A scientist bred fruit flies in two separate containers with different food sources for many generations. When she put the fruit flies from the two containers together again, she observed that the flies preferred mates raised on the same food. Which conclusion can the scientist draw?

A. Fruit flies mate randomly regardless of how they were bred.
B. Fruit flies can adapt to eating different food sources.
C. Fruit flies prefer the container where they were bred.
D. Fruit flies prefer mates adapted to the same food source.

As per the given information in the question, initially fruit flies were in two different containers having different food sources for several generations. Due to this, they got adapted to the specific food sources to which they were exposed. As a consequence, they started preferring mates that were adapted to the same food source.

Therefore, when fruit flies from the two containers were put together, Fruit flies preferred mates adapted to the same food source.

Thus, option D) is the right answer.