_____all the representatives still not there ，the meeting was postponed for several hours.
B
with加名词短语，表示原因，本句意思为：“因为所有的代表还没有到场，会议被推迟了好几个小时”。而because(因为)引导的是原因状语从句，其后必须是个从句。by为“到⋯⋯为止”。
He‘sworkinghard_____.
Thosepeople_____ageneralunderstandingofthepresentsituation.
Itwasnotuntilshehadfinishedallherwork_____.