— If you prefer the red evening dress, you’ll have to pay ________ 30 dollars, because it’s made of silk.— Ok. Here you are.

 We decide to make ________ a rule for us room-mates to turn off the lights at 10:30 pm.

 ---When shall we start, today or tomorrow?---          is OK. You decide.

— ________ have you learned to play the piano?— ________ five years ago.

----How many books are left？ ----                  .