This is a tricky question and perhaps should be worded somewhat differently but let's work with it. From the previous question, we learned that subduction of an oceanic plate underneath the continent is causing earthquake activity. As this oceanic plate dives down into the asthenosphere its leading edge will melt producing magma that will move upwards. Because this magma originates from the oceanic plate it will be predominantly basaltic in nature and thus one would think that basalt should be the answer.

The answer though is andesite. So what is the logic behind this? While there may be some basaltic rock present near the surface in the form of columns, as heat is transferred through the continental plate due to convection, melting will produce andesitic lava and hence andesite is the answer. Then again, one could argue that granite is the predominant rock type for the continents. This is a tough one. For sure, we can say that sandstone is not the answer as it is a sedimentary rock and igneous processes are definitely at work here.