— I telephoned him twice and I couldn’t get through to him.  —The line might have been out of order, _______?

— _______? —She is thirteen.

Reading books is very important for developing the students’ understanding of the world, _______?

What _____ he usually ______ after class?

It was not until the 18th century that man realized that the whole of the brain was involved in the working of the mind，　　　　？