2. (1)What is the connection between our nightly dreams and the actual events that precede them? (2)A naturalistic study of the impact of daytime events on the content of dreams was conducted by researchers shortly after a major earthquake struck the San Francisco area and caused more than $5 billion in damages and killed 62 people. (3)The researchers asked students at two universities in the San Francisco area to keep track of the number of upsetting dreams that they had during a three-week period immediately following the earthquake. (4)As a control group, students at the University of Arizona who had not been near the earthquake did the same thing. (5)Not surprisingly, the students in the area of the earthquake reported more vivid, upsetting dreams then the students in Arizona. (6)In addition, 40 percent of the students in the San Francisco area reported at least one dream about earthquakes, compared with 5 percent of the students in Arizona. (7)Persons exposed to highly stressful events, such as wars, sometimes have nightmarish dreams about them for many years afterwards. (8)Clearly, events and concerns in our daily lives are among the most common things that we dream about. The sentence that expresses the main idea is: