$(6?3) + 4 - (2 - 1) = 5.$ To make this statement true, the question mark between the 6 and the 3 should be replaced by
$\text{(A)} \div \qquad \text{(B)}\ \times \qquad \text{(C)} + \qquad \text{(D)}\ - \qquad \text{(E)}\ \text{None of these}$
Simplifying the given expression, we get: $(6?3)=2.$
At this point, it becomes clear that it should be $(\textrm{A}) \div$.