Complete the sentence with the correct word.They were so on watching the movie that they never heard me ask them a question.

The correct word to complete the sentence is "absent-minded."

So the complete sentence reads: "They were so absent-minded on watching the movie that they never heard me ask them a question."

In this context, "absent-minded" describes a state of being so engrossed in the movie that they were unaware of their surroundings or other events happening around them, such as being asked a question. This term often implies a lack of attention or focus on what is occurring outside of the specific activity in which a person is engaged. The focus on the movie captured their attention to the extent that they became oblivious to other stimuli, which accurately conveys the situation presented in the sentence.