________ is known to all is that effective measures should be taken to deal with the problem of the over­exploitation of our resources.

 I _______ to the party if I________tomorrow.

The pen ______he is writing is mine. 

—____________ difficulty you meet, remember that it might just be a touchstone. —You are right. __________ difficult it is, we will never give in.

   –Do you know _______?--- Someone wants to find his dog back.