Figure 63 Fancy Footwear Manufactures Shoes

Figure 6.3 Fancy Footwear manufactures shoes. Figure 6.3 shows Fancy Footwear's marginal product of labour and average product of labour curves in the short run.
-Refer to Figure 6.3.For what quantity of labour does production display diminishing returns?

A) For more than 1 unit of labour
B) For more than 4 units of labour
C) For more than 5 units of labour
D) For more than 8 units of labour