Which word correctly completes the sentence: "He is known for (stationary, stationery) activities during class."

The correct choice is the word "stationary." In this context, "stationary" means not moving or fixed in place, which is appropriate when describing someone's activities during class that do not involve much movement or change.

On the other hand, "stationery" refers to writing materials, such as paper and envelopes, and does not fit logically within the context of the sentence, as it doesn’t relate to activities performed during class. Therefore, using "stationary" conveys the intended meaning of a lack of movement or activity in class.