What is the hydrosphere and what is its
importance to life on earth

Ch4 and ph3 are both covalent since they are composed both of non-metals.    ch4 is non- polar because of  london forces and has a geometry of tetrahedral  ph3 , on the other hand, is umbrella shaped polar and has dipole-dipole intermolecular force (imf) . since ph3 is polar, it has a stronger imf   

The answer is a, because fossil fuels are burned to make energy, hence the geo (thermal) name.hope this !