11.   Shepherd entered Unity early Wednesday but was forced to retreat when the systems that remove humidity and carbon dioxide from the breathing air of the station broke down.

12.   Supplies of electrical power, breathing air and food, though, are good at least through Wednesday.

13.   That meant that the cooling system and the primary breathing air purification systems were operating.

14.   The electrically driven system that removes poisonous carbon dioxide from the breathing air was reactivated.

15.   The novelist may feel comfortable breathing Parnassian air, but the novel -- his book and the genre itself -- does not.

16.   The three men will rely on the combustion of three lithium perchlorate candles each day to generate sufficient amounts of fresh breathing air.

17.   The systems that cool Mir and remove carbon dioxide from its breathing air were operating Monday.

18.   They also overcame a minor problem with equipment that removes poisonous carbon dioxide from their breathing air supply.

19.   To minimize the health damage, officials are warning hundreds of thousands of people not to leave their homes to minimize their chances of breathing soiled air.

20.   Once she broke out in hives simply by breathing air in an airplane in which peanuts were served.