A.單獨(dú),連續(xù)B.連續(xù),連續(xù)C.單獨(dú),單獨(dú)D.連續(xù),單獨(dú)
A.山頂點(diǎn)B.凹陷點(diǎn)C.平地點(diǎn)D.地底點(diǎn)
A.1個(gè)B.2個(gè)C.3個(gè)D.無(wú)數(shù)個(gè)