BBC news 2011-02-12 加文本

1.It's still too soon to know for certain what made Mr Mubarak step down, but it seems a reasonable assumption that the army leadership could see the hairline cracks appearing among their own officer corps.

but表示转折。assumption that中的that引导的是同位语从句，指代的是assumption。see the hairline cracks appearing，see sb doing sth看到某人正在做某事，看到某事正在发生。

2.It was amid turmoil that Hosni Mubarak became president when his predecessor Anwar Sadat was assassinated in 1981.

it强调句

一、it强调句型的构成：
　　It+be+被强调部分+that(强调部分指人做主语时时用who，指人做宾语时用whom)+句子的其他部分。
　　例如：
　　Mary met an old beggar in the street yesterday.
　　It was Mary who/that met an old beggar in the street yesterday.
　　(强调主语)
　　It was an old beggar whom/that Mary met in the street yesterday.(强调宾语)
　　It was yesterday that Mary met an old beggar in the street.(强调时间状语)
　　It was in the street that Mary met an old beggar yesterday.(强调地点状语)
　　注意：it强调句型不能强调句子的谓语。

二、not…until结构强调句型的构成：
　　It+be+not+until部分+that+句子的其他部分。
　　例如：
　　He didn''t go to bed until his father came back..
　　变为强调句型为：
　　It was not until his father came back that he went to bed.注意原句中的didn''t go部分中的not提前后，剩下did go变为went.
　　本文开头提到的两个句子都是not..until结构用于强调句型。那么把这两句话变回正常的语序则为：
　　1)…but he didn''t make his most important discovery until after the war.
　　2)The importance of Fleming''s discovery was not fully recognized until World War II.