問答題

根據(jù)圖分別說(shuō)明A點(diǎn)與C點(diǎn);B點(diǎn)與C點(diǎn);A點(diǎn)與B點(diǎn)或A點(diǎn)與D點(diǎn)同時(shí)發(fā)生接地時(shí)有什么危害?