Air bags for cars were invented _____ lives. Without them more people would be injured in car accidents.
He tried his best many times._________________, he made his way.
Flying kites, ______ some researchers point out, can not only bring about joy to us, but also promote our physical and mental health.
----Do you know how to learn English well? ________. ----Why? Don’t you think English is quite interesting?
He is really an excellent doctor and he is____to becoming an expert in this field.
One of the tourists ______ from the tour group. That was why the tour guide lost his temper.