问题: Paragraph6_________.
A: Themostimportantsourceofenergy.
B:Typesofelectromagneticenergy
C:Themachinesusedforenergygeneration
D:Seekingnewsourcesofenergy
E:Theuseofultravioletradiationinmedicine
F:Nuclearreactionsasthelastingsourceofthesun’senergy.
