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Sentence Correction: Comparatives - Like/Unlike

Unlike the Gregorian calendar, the synchronization of the calendar year with the astronomical year in the Chinese calendar is not achieved by intercalating a day once every four years, but by adding an intercalary month about once every three years.

Incorrect.

While this answer choice corrects the comparative mistake in the original question, by comparing the Gregorian calendar with the Chinese calendar, it is illogical. By omitting the negation in the original sentence (is not achieved by), it breaks the construction not A but B, making the end of the sentence (but by adding...) illogical.

In other words, this answer choice does not fit the rest of the sentence. Don't forget the final step of the work order!

Incorrect.

This answer choice is grammatically incorrect. This answer choice illogically compares between the Gregorian calendar and the synchronization ... in the Chinese calendar. 

[[snippet]]

Well done!

This answer choice corrects the comparatives mistake in the original question, by comparing synchronization with synchronization.

Although this answer choice is somewhat wordy and awkward, it is the only grammatically correct one and therefore the best one.

Incorrect.

This answer choice is grammatically incorrect. This answer choice illogically compares between the Gregorian calendar and the astronomical year.

[[snippet]]

Incorrect.

This answer choice is grammatically incorrect. This answer choice illogically compares between synchronizing and the Chinese calendar. 

[[snippet]]
Unlike the Gregorian calendar, the synchronization of the calendar year with the astronomical year in the Chinese calendar is not achieved by intercalating
The Gregorian calendar, unlike the Chinese calendar, achieves the synchronization of the calendar year with the astronomical year by intercalating
Unlike the Gregorian calendar, the astronomical year is synchronized with the calender year in the Chinese calender, not by intercalating
Unlike synchronizing the calendar year with the astronomical year in the Gregorian calendar, the Chinese calendar does not achieve this with the intercalation of
Unlike the synchronization of the calendar year with the astronomical year in the Gregorian calendar, this synchronization in the Chinese calendar is not achieved by intercalating