The correct choice is (a) j^e>0
Easiest explanation: If j^e is zero, then a nonzero area element in the real element is mapped into zero areas in the master element, which is unacceptable. Also, if j^e<0, a right-handed coordinate system is mapped into a left-handed coordinate system. In order to keep the element geometries within acceptable distortion, the j^e must be greater than zero, and excessive distortion is avoided.