18. 土石坝施工备用料场储量应为主要料场总储量的 (  )。

、<span>10</span><span>％～</span><span>20</span><span>％</span>

、<span>20</span><span>％～</span><span>30</span><span>％</span>

、<span>30</span><span>％～</span><span>40</span><span>％</span><span> </span>