We regret having to remind you that 20% of the freight is still

We regret having to remind you that 20% of the freight is still _________.
A、owned
B、owning
C、outstanding
D、understanding
【正确答案】：C
【题目解析】：[解析]句意：我们很遗憾地通知您，您还有20%的运费未支付。outstanding表示“未支付的；未完成 的”，符合题意。own表示“拥有”；understanding表示“理解”。