在數(shù)據(jù)流圖(DFD)中,頂層數(shù)據(jù)流圖僅包含一個(gè)( )。A.數(shù)據(jù)處理 B.數(shù)據(jù)存儲(chǔ) C.數(shù)據(jù)流 D.數(shù)據(jù)源或者數(shù)據(jù)匯點(diǎn)