“污染”题

xiangmingliu08

题目大意是说，早在二十世纪， LK 已经被污染了。最近发现雨的数量开始上升，因为排放的污染少了，而且水变清了。现在有些担忧就是，政府要在湖底建oil pipeline，这就有可能再次引起污染. 然而，有种新的科技可以防止油泄漏。所以，在保证这个可以有效的情况下，这些担忧是groundless

问题是：depends on  assuming which one ?
答案是：The bottom of the lake does not contain toxic remnants of earlier pollution that stirred into the water by pipeline construction.

我选的是：Damage to the lake's fish populations would be the only harm that a leak of oil from the pipeline would cause.
因为没有其他因素影响鱼类的树木，所以防止有的泄漏就可以了，这个选项哪里错了？求解！

dengts

please paste the whole problem,including all 5 choices...