多次回声 flutter echo ; multiecho

一次回风 once recycle system ; primary air return

再次回来吧 Come Back Again

一次回路 Primary Circuit ; primary loop ; electric primary system ; primary system

再次回家 Home Again

边界一次回波 Boundary echo

二次回风 secondary return air ; secondary air return

次回路 subloop ; minor loop

一次回线 primary loop

航次/回程租赁 Trip lease/Return trip lease