79. 7-Dehydrocholesterol, a steroid found in skin, is converted into vitamin D3 by two pericyclic reactions. What are these two reactions? (A) 1. an electrocyclic reaction 2. an ene reaction (B) 1. a [1,7] sigmatropic rearrangement 2. an electrocyclic reaction (C) 1. an electrocyclic reaction 2. a [1,7] sigmatropic rearrangement (D) 1. an ene reaction 2. an electrocyclic reaction (E) 1. an ene reaction 2. a [1,7] sigmatropic rearrangement