（二）何谓“所必需的”
在GATT时期，“泰国香烟进口限制和香烟国内税案”的专家组认为，在不存在可合理地期望成员方采取的措施既能实现其健康政策目标，又与GATT基本义务相一致的替代措施，或不存在对GATT基本义务违反程度更低的措施时，成员方的措施才是“必需的”。在“欧共体影响石棉及石棉产品的措施案”中，上诉机构对“所必需的”进行了进一步的阐述：The Appellate Body confirmed that a measure is “necessary” within the meaning of GATT Article ⅩⅩ（b） “if an alternative measure which a Member could reasonably be expected to employ and which is not inconsistent with other GATT provisions is not available to it.” The Appellate Body in EC - Asbestos then considered Canada's claim that the Panel had erroneously found that “controlled use” was not a reasonably available alternative to the measure at issue. In this connection, Canada argued that the Appellate Body itself had held in US - Gasoline that an alternative measure can only be ruled out if it is shown to be impossible to implement. The Appellate Body rejected Canada's argument, but began its analysis by acknowledging that “administrative difficulties” did not render a measure not “reasonably available”. “We certainly agree with Canada that an alternative measure which is impossible to implement is not ‘reasonably available’. But we do not agree with Canada's reading of either the panel report or our report in United States - Gasoline. In United States - Gasoline, the panel held, in essence, that an alternative measure did not cease to be ‘reasonably’ available simply because the alternative measure involved administrative difficulties for a Member. The panel's findings on this point were not appealed, and, thus, we did not address this issue in that case.”[2]