58 . plate used to state the safe height of sign 33 58 .说明标志33的安全高度字牌
2.
New carbon - core aluminum wires can be stretched more tautly than conventional copper wires and so can carry perhaps three times as much current before sagging below safe heights 新型的碳核心铝质线路能拉得比传统铜质线路更长，在安全垂挂高度内可传输的电流大约为以往的三倍。
