B. has与主语Fossils不一致；then与subsequently重复。
C. has与主语Fossils不一致；which非限定性修饰whale错误，应该用非限定性修饰。
D. having been beached，现在分词的完成式having done（主动）不做限定性修饰，只能做非限定性修饰。
E. having beached，现在分词的完成式having been done（被动）不做限定性修饰；then与subsequently重复。
排除法：Fossile 是主语，因此位于用have。排除B，C
既然主谓不缺，中间就为修饰或从句。考虑选项有beached 和 butchered两个谓语。因此选从句。排除D,E。只剩A
感谢由 kisenana 对此题目的解答所做出的贡献。
选项A There are no legal limits on the size of monkfish that can be caught，a circumstance that contributes to their depletion through overfishing.正确
选项B unlike前后比较对象应一致,There are no legal limits on the size of monkfish that can be caught 和cod or haddock不一致
同位语：句中两个逗号隔开，名词开头，那很有可能是同位语。定语描述修饰名词，同位语和这个名词同等地位。
无逻辑表达：efforts have been significant in a reduction of... 努力在减少这件事中是重要的。❌
有逻辑表达：efforts significantly reduced the gap，努力显著减少了差别
1) 宾语从句强调整体, 谓语+宾语结构只强调宾语
2) 对比对象中出现的重复名词用that或those代替,而不能用it来指代. that代替前面出现的单数名词,those代替前面出现的复数名词
3) 修饰成分应该尽量紧靠修饰对象
4) being的错误使用: 以下几种表达中being属于多余
a) being + n. b) being + adj. c) as being + n./adj./v-ing
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B. has与主语Fossils不一致；then与subsequently重复。
C. has与主语Fossils不一致；which非限定性修饰whale错误，应该用非限定性修饰。
D. having been beached，现在分词的完成式having done（主动）不做限定性修饰，只能做非限定性修饰。
E. having beached，现在分词的完成式having been done（被动）不做限定性修饰；then与subsequently重复。
排除法：Fossile 是主语，因此位于用have。排除B，C
既然主谓不缺，中间就为修饰或从句。考虑选项有beached 和 butchered两个谓语。因此选从句。排除D,E。只剩A