A.18;6 B.36;6 C.18;3 D.18;2
A.1 B.2 C.3 D.4
A.向前、向后;牽引、制動(dòng) B.向前、向后;磁場(chǎng)削弱 C.牽引、制動(dòng);磁場(chǎng)削弱 D.牽引、磁場(chǎng)削弱;制動(dòng)