UGAT Bangalore: GrammarTenses. Free, no login required.

By the time the committee arrived, the researchers were completing their presentation, had submitted the report, and left the hall without waiting.

By the time the committee arrived, the researchers completed their presentation, submitted the report, and left the hall without waiting.

By the time the committee arrived, the researchers have completed their presentation, have submitted the report, and were leaving the hall without waiting.

By the time the committee arrived, the researchers had completed their presentation, had submitted the report, and had left the hall without waiting for the panel's feedback.