Elliot works with autistic children and has developed a new app he thinks will improve their ability to track a conversation. He uses the app with the clients he works with at a private school for children with autism. He compare these children's performance in a conversation with peers to the performance of autistic children in the public school who have not used the app. Although Elliot notes that the children who used the app did have better conversational-tracking skills, the fact that they also had access to a higher-quality educational setting than their comparison group threatens the _____ validity of Elliot's conclusions. a. external b. construct c. internal d. predictive