If you don't understand something, you may research, study, and talk to other people _______ you figure it out.
because
though
until
since
Tsinghua University, in 1911, is home to a great number of outstanding figures.
I waited for him at the train station for an hour and I was afraid that he may miss the train, but luckily, he showed up with only ten minutes ______.
Three photos of a school teacher saving two children in a lake have been posted online on October 10, ________ heated discussions on Weibo immediately.
Nuclear radiation is said __________ the biggest health challenge in Japanese Earthquake over the past few months.
Tom’s English is not good, so he devoted all his free time to __________ it.