Some insects________the colour of their surroundings to protect themselves.  

 Isn't it time you got down to ________ the papers?

 She      a golden ring when she searched her old box for a letter.

This book is said to be a special one, which __________ many events not found in other history books．

—I wonder why he has been acting so strangely these days.—Recent pressure at work may     his behavior.