熊女士练习着擦了三次玻璃窗，但收效不大。
Xiong tried to clean the window with the squeegee three times with little success.
有钱人才买得起。所以汽车制造商想方设法提高生产以降低成本，但收效不大。
Only the rich could afford them. So car manufacturers looked around for the ways of speeding up the production so as to reduce the cost but unsucceeded.
长期以来，人们一直采用传统的育种方法来选育高蛋白质的水稻新品种，但收效不大。
Traditional breeding is applied frequently to select new rice varieties with high protein content for a long time but achieved less.
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