When we are very sad,we should think of          .

The sunspot came into its active stage last year,        that happens once every eleven years.

 Computers must be of great use to ________ doing the scientific research. 

September 8th，1931 is a special day，________, I think，that will be remembered by the Chinese forever. 

Don’t worry; we only need _____ 10 minutes to complete the work.