Refer to the graph above Curve A is Ushaped because of A The
     Refer to the graph above.  Curve A is U-shaped because of:  A. The fact that increasing marginal product follows decreasing marginal   
  
  Solution
D. The fact that decreasing marginal product follows increasing marginal product.
Explanation:- Curve A is U-shaped because of law of returns to factor (i.e., law of variable proportion). Intially production is subject to law of increasing returns, then law of constant returns and ultimately to law of diminishing return.

