Suppose that the monodromy for each point $x\in B^{sing}$ is the standard one (see Section 6.4). Then one has two possibilities:

a) $B^{sing}=\emptyset$ and $B=B^{sm}$ is a $2$-dimensional torus;

b) the set $B^{sing}$ consists of $24$ distinct points on the sphere $S^{2}$.