Passage 25
Hotter and more massive than the Sun, stars called “stragglers” are puzzling to astronomers because such rapidly burning stars would not be expected to persist in ancient star clusters. Some researchers believe that the typical blue stragglers formed when two ancient, lower-mass stars collide and merge form more massive, hotter star. Peter Leonard theorizes alternatively that in low density globular clusters, where mergers between single stars occur too infrequently to account for the observed quantity of blue stragglers, these stragglers are created instead by a group of stars. He suggests that a pair of stars already orbiting each other presents a larger target for a third star or another pair. Once this new grouping forms, close encounters between the stars could prompt any two to merge as a blue straggler. Leonard’s model predicts that each blue straggler has a distant orbiting companion—as appears true of many blue stragglers in the M67 cluster of the Milky Way galaxy.
1. The reference to a “larger target” serves primarily to suggest why a
A. blue straggler would be more likely to collide and merge with another star than would be a lower-mass star
B. pair of stars would be more likely to encounter other stars than would the typical blue straggler
C. pair of stars would be more likely to interact with other stars than would a single star
D. blue straggler would be more likely to interact with a pair of stars than it would with a third star
E. third star would be more likely to encounter a pair than it would to encounter a blue straggler
2. Information presented in the passage suggests which of the following about blue stragglers?
A. They originate from stars that are hotter and more massive than the Sun.
B. They are burning more rapidly than other types of stars observed in ancient star clusters.
C. They are older than most other types of stars within the same star cluster.
D. They are less numerous in low-density globular clusters than are pairs of stars.
E. They generally originate from the oldest stars among those found in ancient star clusters.
3. The passage cites which of the following as evidence undermining the theory presented in the second sentence?
A. A discrepancy between the number of mergers between single stars in certain low-density globular clusters and that in other low-density globular clusters
B. A discrepancy between the heat and mass of blue stragglers formed by one type of process and the heat and mass of blue stragglers formed by another type of process
C. A discrepancy between the frequency of star mergers in low-density globular clusters and those in high-density globular clusters
D. A discrepancy between the amount of heat and mass of ancient single stars and that of blue stragglers
E. A discrepancy between the number of mergers between single stars in certain star clusters and the number of blue stragglers in those clusters
答案：C B E
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