看看这个网,
你看清楚一点,这个豆号是在mainly前面的.如果不要豆号.
The depths of the Arctic Ocean are hard to study mainly because the icy surface is difficult to penetrate using current techiniques.这个句子变成run-on了.因为是mainly because,所以还有其他因素的.如果就用because那么the icy suface is difficult to penetrate using current techniques是唯一的因素.那个豆号加上去避免了run-on和保持句子的原本意思.
再问： 我觉得你说的没对啊，“因为是mainly because,所以还有其他因素的” 有些牵强吧。 你发的网站上说的我觉得有道理，“when the sentence begins with a negative proposition” ， 可能就会产生歧义，这点还说的过去，因为我的句子好像就是begins with a negative proposition。不过我没看懂网站上的，能解释一下吗？
再答： 自己领悟一下吧....那个人解释得也不怎么样.也可以说是乱七八糟. 比如"Few adult Romanians speak English because it was forbidden during the Ceausescu era." 很少罗马呢呀人会英文因为它被禁止了. 那它是在说"少数人被禁止说英文,还是英文被禁止了呢?"会有一些冲突.所以隔了会比较清楚. 但你那个和这个没有关联,因为如果不要comma就要写成The depths of the Arctic Ocean are hard to study is mainly because that the icy surface is difficult to penetrate using current techniques.那就会太长了, 用comma隔住了,然而要保持原本意思,就会变成The depths of the Arctic Ocean are hard to study, mainly because the icy surface is difficult to penetrate using current techniques.
再问： 再问一下 我没什么悟性 但真的是太长了？ 谢谢
再答： 恩,真的太长了,你要什么答案啊...
