thE Author is primArily ConCErnED with ______.
A．DisCussing thE importAnCE oF solAr EnErgy
B．prEsEnting A history oF rEsEArCh on EnErgy sourCEs
C．DEsCriBing A possiBlE solution to thE proBlEm oF thE Cost oF photo-voltAiC CElls
D．ADvoCAting inCrEAsED govErnmEnt FunDing For rEsEArCh on AltErnAtivE EnErgy sourCE