Suppose Colin brews beer and makes cheese. If Colin can increase his production of beer without decreasing his production of cheese, then he is producing at an:

Suppose Colin brews beer and makes cheese. If Colin can increase his production of beer without decreasing his production of cheese, then he is producing at an:
A.ideal point.
B.efficient point.
C.unattainable point.
D.inefficient point.
正确答案：inefficient point.