1988年攻读硕士学位研究生入学考试英语试题第Ⅳ大题辨正错误第45小题是这样的: It is encouraging to note that in recent years cigarette smokers have been in the decline, especially among older people. 答案是(C), 改正为 on the decline。
不知这里能否改为 in decline。
on the decline 与 in decline 这两个介词短语的含义是不同的。on the decline 是个成语，意思是：“在减少中”“在下坡路上”“在逐渐衰退”：
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The forces of imperialism are on the decline. (NAECD) 帝国主义的力量正在逐渐衰退。
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In our town, interest in sports is on the decline. (LDCE) 在我们这个镇里,对体育的兴趣正在降低。
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Steel production has been on the decline in these countries. (Mis) 这些国家的钢产量正在逐渐减少。
in the decline of 是指“在……的后期、晚期”，如 in the decline of life(晚年)。
in decline 意为“在衰落中”“走向衰落”：
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I just can't bear Britain in decline. (EED) 我不能容忍英国衰落下去。
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Canon Law was in decline in the tenth and early eleventh centuries. 寺院法是在10世纪和11世纪初走向衰落的。
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With his life in decline, he waited for death. (FWF) 他的生命在垂危之中，他只有等死了。