There __________great changes in our hometown in the past fifteen years.

The research on the new bird flu virus vaccine is challenging and demanding. Who do you think can do the job?—____ my students have a try?

John and Jane are of the same age, but John is taller _______ a head

We ________ contact with each other for years. And last week we ________ contact again.

Goals have to be realistic ________ students can reach them and feel a sense of achievement.