[求助]GWD17-32指代问题

Navigators have known for thousands of years that the ocean has variable currents, but it is only in the last half century that a reasonably clear picture has emerged of the patterns and causes of ocean currents.

1. a reasonably clear picture has emerged of the patterns and causes of ocean currents
           
2. a reasonably clear picture of the patterns of ocean currents and their causes have emerged
           
3. a reasonably clear picture emerged of ocean currents, their patterns and the causes of them
           
4. there have emerged a reasonably clear picture of the patterns of ocean currents and what caused them
           
5. there had emerged a reasonably clear picture of the patterns of ocean currents and their causes

答案A  偶想问问各位nn   B除了主谓不一致的错误外 their的指代有问题么

我觉得似乎有点疑问就是，到底是指示patterns 还是 currents

对呀

如果是 N(1)'sN(2).......it 那么it只能指N（2）

如果是 N（1） of N(2)......it 可以指代N（1）或N（2）

但不知道 N(1)'sN(2).......its 和 N（1） of N(2)......its的情况要怎么算？

感觉their指代没有问题 只是causes 不能emerge

thank you~~

那时说N(1)'sN(2).......its 中 its只可以指代N（1）

和 N（1） of N(2)......its中its只可以指代N（2）么