Which of the following statements about stellar spectroscopy is wrong?

A、Spectraltypesaremainlydividedintosevencategories:O，B，A，F，G，K，M.;
B、Eachspectrumcanbedividedintotensubtypes.;
C、B0andO9areverydifferent.;
D、O,B,Aareearlytype,F,Garemediumtype,K,Marelatetype.