Ireland has the following demographic features except().
A. it has a low birthrate
B. it has a late marriage age
C. it has an excess of females in the population
D. it has a high proportion of bachelors and spinsters of all age
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精馏塔的进料为饱和气液混合物时,进料线的斜率q/(q-1)为()。
某滚子链“12A-2×84 GB1243-83”各数字符号说明什么?