21.It is required that the composition _________to the students’ life.
A．should relate B．must relate C．is related D．be related
22. I like getting up very early in summer. The morning air is fresh____.
A. to be breathed B. to breathe C. breathing D. being breathed
23. _________to sunlight for too much time will do harm to one's skin.
A．Exposed B．Having exposed
C．Being exposed D．After being exposed
