He began to take political science_____ only when he left school. 

The earthquake in Yushu, Qinghai Province damaged many houses and business buildings； _______, it caused more than 1,000 deaths.

Nowadays, Chinese consumers are increasingly aware of their rights.       , safety and quality issues remain top concerns.

My boss hates interruptions,       when he is trying to work.

I wasn’t blaming anyone: I ________ said errors like this could be avoided.