$\begin{array}{1 1}(a)\;sp^3 - sp^3 < sp^3 - sp^2 < sp^3 - sp < sp^2 - sp^2\\(b)\;sp^2 - sp^2 < sp^3 - sp < sp^3 - sp^2 < sp^3 - sp^3\\(c)\; sp^3 - sp < sp^2 - sp^2 < sp^3 - sp^2 < sp^3 - sp^3\\(d)\; sp^2 - sp^2 < sp^3 - sp^3 < sp^3 - sp^2 < sp^3 - sp\end{array}$