during；     unless；     sky；     time；     arrive；      proper；     put up

（1）Hurry up， Harry．Our friends 　　in half an hour．

（2）I usually sleep with the window open 　　it's really cold．

（3）There we 　　tents and made a fire to keep us warm．

（4）The students who are good at writing can always use words 　　．

（5）Because of the good environment， it is easy for us to see the blue 　　now．