单项选择题

A.Transactionmanagementisblock-orientedratherthanwindow-oriented.
B.Formsautomaticallynavigatestoanitemlocatedinanactivatedwindow.
C.Awindowmaycontainmultipleblocks,buteachblockcanonlyspanonewindow.
D.Awindowcancontainmultiplecanvases,andanitemcanbelocatedonmultiplecanvases.