$\begin{array}{1 1} (a)\; \text{30-100 km, silicate rocks} \\ (b)\; \text{100-150 km, magnesium rocks} \\ (c)\; \text{40-120 km, silicate rocks, iron and magnesium} \\ (d)\; \text{5-70 km, silicate igneous rocks} \end{array}$
