在酸、碱、盐、氧化物中许多物质相互反应生成盐类物质，如图①②③④组合中都能生成盐类物质．

根据表中提供信息，完成下列问题．

（2）写出反应③中能生成CaCO₃化学方程式．

（3）小华同学想利用组合④反应制KNO₃，选用的药品是NaNO₃和KOH能否达到目的？为什么？

Dina Borzekowski made a study of a group of third-grade students from six American schools. During a school year, nearly 400 students and their parents were asked to report on whether they had such things as televisions and computers in the home, as well as how often the child used them. The children’s language ability was tested (测验) twice over the year. Children who had a television set in the bedroom but did not have a computer at home scored (得分) the lowest, while students without TV in the bedroom but with a computer at home scored the highest. Students who had a television in the bedroom over the school year scored lower than those who had their TV taken away during the same time.
"This study suggests that taking TV sets out of children’s bedrooms, or not putting them there, may be helpful," said Borzekowski. "While this study does not prove (证明) that bedroom TV was the reason for the lower test scores, it suggests that children shouldn’t have TV in their bedrooms. It also suggests that a home computer may help a child’s test scores. The best way was having both: no TV in the bedroom and also a home computer to use. \

How long did Borzekowski’s study last
[A] One year.
[B] Three years.
[C] Six years.