_________ environmental damage is done, it takes many years for the ecosystem to recover.
| A．Even if | B．If only | C．While | D．Once |
I like to do everything .
| A．personally | B．on her own |
| C．by herself | D．All of the above |
No matter when I look my miserable past, I feel sad and sorrowful.
| A．back | B．on |
| C．back on | D．upon |
They separated ten years ago and never met againthen.
| A．by | B．from |
| C．ever | D．since |
The disabled _____down upon in the past .
| A．was looked | B．were looked |
| C．looked | D．did look |
If you _____a crime you can never escape being punished.
| A．commit | B．discharge免除（自己的义务、负担等）； |
| C．take | D．do |