As mines age, ore grades decline, since the best stuff is usually dug up first.
随着矿山年龄的增长，铁矿石的等级下滑，因为最好的往往被最先发掘。
As older mines get deeper, ore grades decline and extraction becomes more expensive.
随着旧矿越挖越深，矿石的品质下降使提取成本增加。
Records show that during December and January, the two months with the fewest hours of daylight, attendance rates fall, average daily class participation drops, and grades decline.
记录表明在日光最少的十二月和一月，出席率下降，每日平均课程参加量减少，分数降低。
Results : Under the slit lamp , with the increasing of haptic angulation of IOL implanted , it showed a decline in the number and the grades of PCO.
结果：裂隙灯显微镜下可见术后随着人工晶体袢角度的增加，发生后发性白内障的例数及等级均呈下降趋势。
Results : Under the slit lamp , with the increasing of haptic angulation of IOL implanted , it showed a decline in the number and the grades of PCO.
结果：裂隙灯显微镜下可见术后随着人工晶体袢角度的增加，发生后发性白内障的例数及等级均呈下降趋势。
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