  For a knot $K$ in a homology $3$-sphere $\Sigma$, let $M$ be the result of
$2/q$-surgery on $K$, and let $X$ be the universal abelian covering of $M$. Our
first theorem is that if the first homology of $X$ is finite cyclic and $M$ is
a Seifert fibered space with $N\ge 3$ singular fibers, then $N\ge 4$ if and
only if the first homology of the universal abelian covering of $X$ is
infinite. Our second theorem is that under an appropriate assumption on the
Alexander polynomial of $K$, if $M$ is a Seifert fibered space, then $q=\pm 1$
(i.e.\ integral surgery).
