For some people, the sight of a mouse can be reason to scream. For other mice, the same sight can be reason to sing.
Mice will probably   21   sing their way to any concert, but researchers in the United States have found   22   that mice do,   23  , sing.
Scientists already knew that mice make ultrasonic(超声波) sounds—noises that are too high-pitched(高音的) for people to hear   24   special equipment.
To find out whether mice put such sounds together in song-like   25  , the researchers recorded the sounds of 1 mice. Using computer   26  , they were able to separate the sounds into specific types of syllables(音节), and found the mice produced about 10 syllables per second.
The results showed that nearly all of the mice repeated sequences(顺序) of syllables in different patterns. That’s enough to meet the definition of what scientists   27   song. But not all scientists are   28  _ that what the mice are doing is   29   singing. To prove it, the researchers must show that there’s learning involved. And, they need to __  30   why the mice sing.
21. A. almost                     B. even                       C. never                     D. usually
22. A. coincidence   B. evidence              C. guidance              D. instance
23. A. at once          B. by means             C. for example D. in fact
24. A. during                      B. inside                     C. through                D. without
25. A. fashions                  B. instructions C. patterns               D. styles
26. A. access                     B. printer          C. screen          D. software
27. A. call                            B. hear                       C. sing                        D. write
28. A. accustomed  B. convinced            C. involved                D. qualified
29. A. actually           B. obviously              C. simply          D. unlikely
30. A. figure out               B. get about             C. run across           D. talk over