Rare species in the world, ______ by hundreds every year, must be jointly preserved by all countries, or humans will encounter ecological disaster in the near future.

 ______ on ten years of observation and study, the theory shows that every one dreams every night, whether they realized it or not.

 Our waste recycling project ________ a lot of investigation and paperwork had been done by the end of last term.

I’ m not used ____ like this .

His first book ___________ next months is based on a true story.