1 . Have you ever wondered why certain pop songs just make you feel so good? Researchers studying the question found that uncertainty and surprise give listeners the most pleasure. The study included 80,000 chords（和弦）in 745 pop songs between 1958 and 1991.

Each song was stripped of its melody（旋律）and lyrics（歌词）so that only chords were left and the results couldn^’t be misunderstood by other imaginations of the songs that listeners might have had.

They found two things. Listeners got great pleasure from unexpected chords when they knew what would happen. However, they still found it pleasant to hear familiar chords when they did not know what would follow.

Vincent Cheung, the lead researcher, said, "Pleasant songs are likely those which keep a good balance（平衡）between knowing what is going to happen next and surprising us with something we did not expect. Understanding how music starts our pleasure system in the brain could explain why listening to music might help us feel better when we are feeling blue.”

Cheung told CNN that pleasure in music is connected to expectation. The study before had looked into the effects of surprise on pleasure, but his team's study also paid attention to the uncertainty of listeners' expectations.

1. What does the underlined word in Paragraph 2 mean?

A．Removed.	B．Added.
C．Played.	D．Recorded.

2. How did the researchers do the research?

A．They listened to lots of pop songs.

B．They focus on the chords in popular songs.

C．They imagined the songs that can make people pleased.

D．They found lots of songs and then compared each other.

3. What can we learn from the passage?

A．Pleasant music can explain human nature.

B．Listening to music might make people feel blue.

C．Music can improve the pleasure system of people.

D．Pleasant music comes from the balance of expectation and surprise.

4. What is the difference between Cheung's study and others' study?

A．His study only paid attention to chords in songs.

B．His study focused on the effects of surprise on pleasure.

C．His study took time to how music starts the pleasure system.

D．His study paid attention to the uncertainty of listeners' expectations.