Country1- Pair1-industry1-time1为dummy1
Country1- Pair1-industry1-time2为dummy2
...
Country1- Pair1-industry1-timen为dummyn
Country1- Pair1-industry2-time1为dummy21
Country1- Pair1-industry2-time2为dummy22
...
Country1- Pair1-industryn-timen为dummy2n
...
理论上会产生n*n*n*n个dummy