大家可以帮我看一下我这个命令哪里错了吗？？xtivreg2 (D.capr=solvency  D.prisk D.arisk L.capr rein size roa lr hdi type)(D. arisk=solvency D.capr D.prisk L.arisk rein size lr leverage  hdi type)(D.prisk=solvency D.capr D.arisk L.prisk rein size lr leverage  hdi type)，fe
老是出现error - must specify either fe or fd option
invalid syntax