optionallyadv.可选择地optionaladj.任选的optional switched channel任选开关通道optional half instruction任选半指令optional and open running自选开放式optional local peripheral任选局部外围设备optional stop instruction选择停机指令, 条件停机指令optional athletic classes体育选项课optional resident routine随意驻留例行程序Optionally Piloted Vehicle随意驾驶飞行器optional routing algorithm任选路径选择算法optional pause instruction可选停机指令