BBC news 2010-04-18 加文本

1.And the reason why the glacial ice is so important is that the glacial ice is responsible for quenching the lava that's appearing at the eruption site.

reason 的用法应注意以下几点：
 
1)表示理由或原因，多用作可数名词，有时也用作不可数名词，其后常接介词for-短语或不定式短语：
Give me your reason (s) fordoing it. 说说你做这件事的理由吧。
I have many reasons tofear him. 我怕他是有很多理由的。
There is (some) reason tosuspect him. 怀疑他是有 (些)理由的。
The reason for the floodwas all that heavy rain. 涨洪水的原因完全是那场大雨。

2)后接定语从句，用why (=for which)引导，有时也可用that, 在非正式英语中甚至可以省略：
The reason that [why] he died waslack of medical care. 他死的原因是缺少医疗。
The reason I didn’t tell you was that I wanted it to be a surprise. 我之所以没有告诉你是想让它给你个惊奇。
注意the reason之后所接的why引导的定语从句，必须是限制性的，而不能是非限制性的。

3)在 The reason why…is that…这类句型中，通常要用 that来引导表语从句，但在现代英语中用 because的情况已比较普遍：
Thereason (why) he did not come was that [because] he was ill. 他没有来是因为他生病了。
但在应试中，若要从that / because中作出选择，当然以选that为宜。

2. The government has been pressing the companies to give up concessions that give them a share of profits from oil fields and to accept service contracts instead.

that give them a share of profits是定语从句，修饰concessions。to give up和to accept是两个并列的成分，都是pressing的内容。