There_______a teacher and some students on the playground.

His younger sister may already be in high school now, in ________ case this picture book is too childish for her.

The manager entered the office and was happy to learn that four-fifths of the tickets ______. [ ]

________ thank you too much for all your help to my son while we were away from home.

Email is very popular today. People ______write letters to each other now.