按照张老师的多期平行趋势检验的代码修改了一下做的结果显示，
warning: year might be perfectly explained by fixed effects (tol = 1.0e-09)
(MWFE estimator converged in 2 iterations)
warning: missing F statistic; dropped variables due to collinearity or too few clusters
note: eventz2 omitted because of collinearity
note: eventz3 omitted because of collinearity
note: eventz4 omitted because of collinearity
note: eventz5 omitted because of collinearity
note: eventz6 omitted because of collinearity
note: eventz7 omitted because of collinearity
note: eventz8 omitted because of collinearity
note: eventz9 omitted because of collinearity
note: eventz10 omitted because of collinearity
note: eventz11 omitted because of collinearity
note: eventz12 omitted because of collinearity
note: eventz13 omitted because of collinearity
note: eventz14 omitted because of collinearity
note: eventz15 omitted because of collinearity
note: eventz16 omitted because of collinearity
note: eventz17 omitted because of collinearity
note: eventz18 omitted because of collinearity
note: lofdiflow1 omitted because of collinearity
note: lifdiflow1 omitted because of collinearity
note: lofdistock1 omitted because of collinearity
note: lnet_export omitted because of collinearity
想问下，是哪里除了问题