The average of the two middle rational numbers, if \[\frac{4}{7},\frac{1}{3},\frac{2}{3},\frac{5}{9}\] are arranged in ascending order is ____.

• A. \[\frac{4}{9}\]
• B. \[\frac{71}{63}\]
• C. \[\frac{2}{9}\]
• D. \[\frac{71}{126}\]