Every day in the morning Ross cycles for 2 hours. He always starts at a constant rate of 1 mile of distance in every 12 minutes. However, he takes a different path for onward and return journey – the distance covered in the return journey is double of the distance covered in his onward journey. Also, his speed in the return journey becomes half of his original speed. What is his average speed on the whole journey?

A. 3 mph
B. 4 mph
C. 5 mph
D. 6 mph
E. 7 mph

[spoiler]OA=A[/spoiler]

Source: e-GMAT