Classification is a useful ______ to the organization of knowledge in any field.

A．means

B．approach

C．mode

D．manner

根据《低压配电设计规范》，起重行车上方的裸导体至起重行车平台铺板的净距不应小于（）

A.2.3m

B.2.4m

C.2.5m

D.2.6m