He is busy preparing a secret present for his Mum, ______ is cheap but special.

We are confident that the step the Chinese government has taken to cope with the current crisis is ______ of great significance.

—What’s wrong with me, doctor?—        serious. Just a slight cold.

The chairman thought _____ necessary to invite Professor Smith to speak at the meeting.

Nine in ten high school students say there are significant differences in their attitude toward chatting on line, compared with _________ of their parents.