题目内容：
Imagine that the world consists of 20 men and 20 women, all of them heterosexual and in search of a mate．Since the numbers are even, everyone can find a partner．But what happens if you take away one man? You might not think this would make much difference．You would be wrong，argues Tim Harford，a British economist， in a book called The Logic of Life． With 20 women pursuing 19 men, one woman faces the prospect of spinsterhood． So she ups her game． Perhaps she dresses more seductively． Perhaps she makes an extra effort to be obliging． Somehow or other, she “steals” a man from one of her fellow women． That newly single woman then ups her game, too, to steal a man from someone else． A chain reaction ensues． Real life is more complicated, of course, but this simple model illustrates an important truth．In the marriage market, numbers matter．And among African-Americans，the difference is much worse than in Mr．Harford's imaginary example．Between the ages of 20 and 29, one black man in nine is behind bars．For black women of the same age, the figure is about one in 150．For obvious reasons, convicts are excluded from the dating pool．
Removing so many men from the marriage market has profound consequences．As imprisonment rates exploded between 1970 and 2007， the proportion of U.S.-born black women aged 30-44 who were married plunged from 62%to 33%．Why this happened is complex and furiously debated．The era of mass imprisonment began as traditional mores were already crumbling， following the sexual revolution of the 1960s and the invention of the contraceptive pill．① It also coincided with greater opportunities for women in the workplace． These factors must surely have had something to do with the decline of marriage．
But jail is a big part of the problem, argue Kerwin Kofi Charles, now at the University of Chicago． They divided America up into geographical and racial “marriage markets”, to take account of the fact that most people marry someone of the same race who lives relatively close to them．② Then, after crunching the census numbers， they found that a one percentage point increase in the male imprisonment rate was associated with a 2.4-point reduction in the proportion of women, who ever marry．③ Could it be, however, that mass imprisonment is a symptom of increasing social malfunction, and that it was this social malfunction that caused marriage to wither?④ Probably not. For similar crimes, America imposes much harsher penalties than other rich countries．Mr. Charles and Mr. Luoh controlled for crime rates, as a substitution for social malfunction, and found that it made no difference to their results. They concluded that “higher male imprisonment has lowered the likelihood that women marry...and caused a shift in the gains from marriage away from women and towards men.”
阅读以上文章，回答题
The word “ensues” in Paragraph 1 probably means __________．
[A] to result in something
[B] to happen after something<
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