During crane operation, if the operator is engaged in a lift and needs to leave the controls, they must:

解析

The rule is flat: the operator does not leave the controls while the load is suspended, and no suspended load is left unattended. Each wrong answer tries to make leaving safe and covers only one failure mode. Setting the brake (a) trusts a mechanical hold against wind, drift and hydraulic creep, and leaves nobody able to respond if the load starts to move. Clearing the crew (c) and barricading beneath (d) deal with the load coming straight down, but a suspended load can also swing into the structure, and conditions can change - a gust, a settling outrigger - while nobody is at the controls to correct it. The only answer the standard accepts is to land the load first.