Final answer:
Correct answers for the true statements about task functions include that effective teams perform task functions as required and that teams that execute these well tend to perform better. The importance of different task functions may fluctuate over the course of the team's development.
Step-by-step explanation:
Regarding the true statements about task functions, teams indeed perform better when completing task functions effectively. This is because effective teams have members who address and perform these functions as needed (Option A and Option B are correct). Tasks functions relate to the specific actions taken by team members to complete their goals or objectives, which can vary in importance throughout the team's development; therefore, Option D is also correct. However, the proficiency in performing task functions doesn't necessarily imply that the team will also excel in maintenance functions, which are related to emotional and social aspects within the team (Option C is not necessarily true).