GMAT Reading Comprehension (RC) | Re: In an attempt to improve the overall performance of clerical

In 2nd D & E are very close . Didn't get why D is preffered over E . As per the passage :

However, at least one study has shown that such monitoring may not be
having the desired effect. In the study, researchers asked monitored clerical workers and their supervisors how assessments of productivity ..........

Since , it is not desired effect and it happened , please explain .

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