GMAT Sentence Correction (SC) | Re: Although hand-written letters may convey personal

Lack of parallelism:

The compared elements are:

X: writing letters takes effort
Y: it does for emails (it takes for emails).

The elements are not parallel. In order to use Y in the form it is in, X should have been:

X: it takes effort for writing emails

The correct usage then would be:

... it takes far more effort for writing letters than it does (takes) forwriting emails.

Nonetheless, idiomatically
...

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