Since reform and opening-up
例句：
改革开放以来,中国经济生活中出现了一个特殊现象农民工问题.
Since reform and opening-up,the special phenomenon of farmer workers has appeared in china's economic life.
改革开放以后各民族的人员交流增多了.
Since reform and opening-up,exchanges between the people of various nationalities have increased.reform and opening-up相当于专有名词，不需要加the. 正如China不需要加the，因为世上只有一个China。