With our knowledge ________ practice, we can make contributions to our society [ ]

What about the books ?—Books of this kind _____ well .

The playground ____ we built last year is very large.

The sun ___ we get heat and light is the most important source of energy.

Do you know the reason _________ pilotsturn off the plane’s lights before taking off —The practice is for the passengers toadjust to the dark _________ an emergency