This is the 637th most frequent Chinese word.
先后
"One after another; order or sequence."
'先后' here denotes actions happening in a sequential manner, implying that the competition was completed first, followed by the task.
他们先后完成了比赛和任务。
They completed the competition and the task successively.
'先后' in this sentence emphasizes the chronological order of his speeches during the meeting.
会议期间他先后发了三次言。
During the meeting, he spoke three times one after another.
'先后' here indicates a sequence of events, where the visits to the countries occurred consecutively over a period.