The retired workers were invited to the company， ________surprise，changes had been so great over the years.

If anyone happens to drop in while I am out, _________ him or her leave a message.

arents encourage their children totake an active part in social events, ______ those events do not interfere withtheir studies

It _______to John that he had left the doorunlocked.

________ is mentioned(提及) above, the number of the students in senior high schools is increasing.