Even though she        much, the woman multimillionaire insists on working as a street cleanser to set her children a good example.

______ the plan means we must start from the very beginning. 

By the time he realizes he _____ a mistake, it’ll be too late for him to change his mind.    

The old man __________ in Tibet for two years as a volunteer teacher；it is an experience he  often mentions.

--You speak very good French! ---Thanks. I _________ French in Sichuan University for four years.