Countermeasures: fair use, temperance drug use, develop the risk-benefit ratio, low residue and selective pesticides.

对策：公道用药，节制用药，研制高效低毒，低残留并有选择性的农药。

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Selective suitable conditions such as the ratio of reactions, different catalyst and the addition of dehydrater etc are presented. The result which is the yield of product is 82.5%.

选择了合适的原料配比、催化剂、脱水剂用量等反应条件，反应所得到的丙酮酸乙酯收率为82.5%；

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Ratio of ethylene to propylene can be regulated through selective hydrogenation, separation and disproportionation. Requirements on some key parameters are pointed out and the reasons are discussed.

通过选择加氢、分离和歧化反应调整乙烯和丙烯产品的结构比例，指出了对部分主要操作参数的控制及要求，并分析了其原因。

youdao

There, selective poaching of males has led to a dramatic skew in the sex ratio.

NPR: Lifting the Ivory Ban Called Premature