In rolling, the metal would not enter the space between the rolls automatically if the angle of contact

Question

Which one of the following is correct?

In rolling, the metal would not enter the space between the rolls automatically if the angle of contact  

(a) $< \tan ^{-1}\mu$

(b) $> \tan ^{-1}\mu$

(c) $> \frac{1}{2}\tan ^{-1}\mu$

(d) $< \frac{1}{2}\tan ^{-1}\mu$