gwd25 39求助

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.
A a reasonably clear picture has emerged of the patterns
 and causes of ocean currents.
B a reasonably clear picture of the patterns of ocean
 currents and their causes have emerged.
C a reasonably clear picture emerged of ocean currents,
 their patterns and the causes of them
D there have emerged a reasonably clear picture of the
 patterns of ocean currents and what caused them.
E there had emerged a reasonably clear picture of the
patterns of ocean currents and their causes.

几个of 搞得我头都晕了,没看明白到底是在说什么意思.

答案是 A, 麻烦给我讲讲吧.

I see now, the original statement should be like this:

 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 of the patterns and causes of ocean currents has emerged.  

But b/c the bold faced part is too long, so they switch it to the end. That's why choice A is correct.

thanks for the good question!qingqinghu

mbz明白了?那麻烦你给我翻译一下这个划线部分吧.

我不理解的就是那个中间的几个of 的关系.

I will try to explain it in English here:

For thousands of years, navigators have known that there are different kinds of currents, but they did not understand and did not have a clear picture of the patterns of those currents, until the last 50 years.

qingqinghu, does that make sense to you now?

Could someone please type it in Chinese? otherwise it will cost me 30 minutes to do so.

picture of the patterns and causes of ocean currents
        

洋流的来龙去脉图， causes = 成因