设某商品的市场需求函数为Q=1-P/7,p为商品价格,则需求弹性函数为()。
A <img src="https://www.beizhujiaoyu.com/uploads/202208/161191192837851.png" width="41" height="34" /> B <img src="https://www.beizhujiaoyu.com/uploads/202208/161191193378211.png" width="41" height="38" /> C <img src="https://www.beizhujiaoyu.com/uploads/202208/161191193728441.png" width="42" height="32" /> D <img src="https://www.beizhujiaoyu.com/uploads/202208/161191194392181.png" width="41" height="35" />