questions 31 to 35 are based on the following passage:
priscilla ouchida’s “energy-efficient” house turned out to be a horrible dream. when she and her engineer husband married a few years ago, they built a $100,000, three-bedroom home in california. tightly sealed to prevent air leaks, the house was equipped with small double-paned（双层玻璃的）windows and several other energy-saving features. problems began as soon as the couple moved in, however. priscilla’s eyes burned. her throat was constantly dry. she suffered from headaches and could hardly sleep. it was as though she had suddenly developed a strange illness.
experts finally traced the cause of her illness. the level of formaldehyde（甲醛）gas in her kitchen was twice the maximum allowed by federal standards for chemical workers. the source of the gas? her new kitchen cabinets and wall-to-wall carpeting.
the ouchidas are victims of indoor air pollution, which is not given sufficient attention partly because of the nation’s drive to save energy. the problem itself isn’t new. “the indoor environment was dirty long before energy conservation came along,” says moschandreas, a pollution scientist at geomet technologies in maryland. “energy conservation has tended to accentuate the situation in some cases.”
the problem appears to be more troublesome in newly constructed homes rather than old ones. back in the days when energy was cheap, home builders didn’t worry much about unsealed cracks. because of such leaks, the air in an average home was replaced by fresh outdoor air about once an hour. as a result, the pollutants generated in most households seldom build up to dangerous levels.