A、100 percent. B、99.9 percent. C、90.9 percent. D、90 percent. B录音中提到：“filters out 99．9percent of the salt”(过滤掉99．9％的盐分)，由此可知B项正确。

(22)California is in the midst of the worst drought on record, and yet the need for freshwater is only increasing. In order to meet that demand, cities across the state are turning to rather controversial and expensive technology called desalination, where they turn ocean water into freshwater.(23)Fifteen desalination plants are currently in the works in California , the largest being the 1 billion Carlsbad plant slated to open this November.(24)When operational , it will produce 50 million gallons of fresh water a day through a process called reverse osmosis, which filters out 99. 9 percent of the salt. We certainly didn’t plan on completing the plant during record drought conditions here in California, but it does highlight the importance of what we’re doing, which is to provide a new supply of water, essentially drought-proof water. But this drought-proof water source comes at a price. The desalination process is incredibly energy-intensive and the water produced from the plant will cost about twice as much as traditional tap water. A gap the San Diego Water Authority expects will close overtime. Up the coast, Santa Barbara is planning to invest 40 million to reactivate a plant that was built in the 90s, during the state’s last severe drought. The plant ran for just four months before heavy rains ended the dry spell. Over 30 million investment, only use for four months and then sits here for 23 years.(25)Desalination is expensive. But if you start to look at the economic impacts of a community running out of water, it will dwarf any costs of bringing desalination to this community. The city says it will take about 12 to 14 months to update the now very outdated facility.
Questions 22 to 25 are based on the passage you have just heard.
22. Why do cities in California turn ocean water into freshwater?
23. How many desalination plants are in operation now in California?
24. How much of the salt is filtered from seawater by desalination plant?
25. What’s the speaker’s attitude toward desalination?