Start with the theorem "If two angles of a triangle are equal, the triangle is isosceles," and the following four statements:
1. If two angles of a triangle are not equal, the triangle is not isosceles.
2. The base angles of an isosceles triangle are equal.
3. If a triangle is not isosceles, then two of its angles are not equal.
4. A necessary condition that two angles of a triangle be equal is that the triangle be isosceles.
Which combination of statements contains only those which are logically equivalent to the given theorem?
<spanclass=′latex−bold′>(A)</span>1,2,3,4<spanclass=′latex−bold′>(B)</span>1,2,3<spanclass=′latex−bold′>(C)</span>2,3,4<spanclass=′latex−bold′>(D)</span>1,2<spanclass=′latex−bold′>(E)</span>3,4