季节虚拟变量现在搞定了，确定性趋势怎么办呢？

are you sure 't' will change in the same proportion every season? If so, i think it would be ok to set t = 1,2,3,4,5...., or you may spend some time on 't' first.

我现在不设季节虚拟变量了，改成把其中一个自变量，和应变量一起做季节调整了，这样可以吗？

i am interested in how you will do the seasonal adjustment. I think one way to test whether t is a stable trend could go for testing whether y(t)-y(t-1) is convergent.

I think your previous model is more straightforward.Seasonal Dummy Varable could be applied by assigning value of 1,2,3,4 for each period.

我最后没有搞季节虚拟变量，我考察的是本年的价格和上年的价格、还有其他一些变量的关系，所以我就直接把上年的价格按月放到里面了。趋势我就按年取。