There are some health problems that, when in time, can become bigger ones later on.
Mary speaks in a low voice; ____ is difficult to know what she is saying.
Was it because he was ill ____ he asked for leave?
It was on October 1st ____ new China was founded.
It was in the rice fields ____ we had our league meeting.
It was through Xiao Li ____ I got to know Xiao Wang.