ACCorDing to thE gErmAn rEsEArChErs, thE EnErgy sourCE At thE CEntEr oF thE milky wAy gAlAxy ______.
A．hAs BEEn CovErED up By vAst ClouDs oF Dust AnD gAs
B．still rEmAins unknown to AstronomErs
C．hAs provED to BE A BlACk holE
D．ACtuAlly proviDEs powEr For thE rotAtion oF FilE grEAt spirAl oF stArs