Answer: D. "none."
Step-by-step explanation: The complement of "at least one" is "none."
When we say "at least one," it means that there is a minimum of one of something. Therefore, the complement of "at least one" refers to the opposite condition, where there is no occurrence of that something.
Here's an example. Suppose you have a bag of marbles, and you are told that the bag contains at least one red marble. The complement of "at least one red marble" would mean that there are no red marbles in the bag.