The following is output data for a firm. Assume that the amount of all non-labour resources are fixed.

Number of Workers Units of workers output

0 0

1 40

2 90

3 145

4 160

5 165

6 167

Refer to the above information. Diminishing returns become evident with the addition of:

a) the fourth worker.

b) the third worker.

c) the second worker.

d) the first worker.