This is how I diagrammed it:

whoever is kind is loved by somebody or other (K->loveD)

whoever loves anyone is happy (loveS->H)

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it follows that whoever is kind is happy (K->H)

so to arrive at the conclusion we would need to connect loveD->loveS.

answer choice D is /loveS->/loveD

the contrapositive of this would become loveD->loveS, exactly what we need!

as for answer choice E, it would be loveS->K, but we would need K->loveS in order for this to be relevant.

Wow just learning the difference boosted my score up in LR by 2-3 points!

I personally think its doable, but it also depends on the question types you are getting wrong. If you are mainly getting the games section wrong, it is very easy to achieve a higher score in a relatively shorter period of time, since the games section are the easiest to 'learn' by repetition. However, if it is the RC section, more time should be devoted I think.