Which of the followings are true for ridge lines?

A. they separate the relevant from the irrelevant portions of the isoquants

B. along the ridge lines, the slope of the isoquants is either zero or infinite

C. The relevant segment of the isoquants enclosed pertains to the stage II of production for labour and capital

D. Producers will never want to operate outside the region enclosed within the ridge lines.

E. The marginal product of both inputs-labour and capital is positive but declines for the portion of the isoquants within the ridge lines.

Choose the correct answer from the options given below: