If two rods of length L and 2L having coefficients of linear expansion \[\alpha \] and \[2\alpha \] respectively are connected so that total length becomes 3L, the average coefficient of linear expansion of the composite rod equals :

• A. \[\frac{3}{2}\alpha \]
• B. \[\frac{5}{2}\alpha \]
• C. \[\frac{5}{3}\alpha \]
• D. none of these