optionallyadv.可选择地optionaladj.任选的optional user facility可选用户机制optionally substituted可选被取代optional decision rule最佳决策律optional P.E. class体育选项课Optional Team Targeting小分队选择性目标瞄准optional bill of lading任选港提单,选择港提单,选港提单optional public modules公共选修课optional printable area任选可印面积optional transformation随意转换optional stowage clause任意装载条款