将下面改写的学术、精炼一点Firstly the robustness test is carried out by replacing explanatory variables and explanatory variables 1 Referring to Lu and Lian 2012 the total factor productivity TFP representing the

Firstly, we conduct a robustness test by substituting different explanatory variables. Following the approach of Lu and Lian (2012), we calculate the total factor productivity (TFP) using the fixed effect method, LP method, and OP method. The input indicators selected include capital, labor, investment, and intermediate input, while the output indicator used for regression is operating income. The results are presented in columns (1)-(3) of Table 2.