In 1860, the Philological Society launched its effort to create a dictionary more comprehensive than the world had ever seen; although the project would take more than 60 years to complete, the Oxford English Dictionary had been born.
A would take more than 60 years to complete, the Oxford English Dictionary had been
B took more than 60 years to complete, the Oxford English Dictionary was
C would take more than 60 years to complete, the Oxford English Dictionary was being
D would take more than 60 years to complete, the Oxford English Dictionary was
E took more than 60 years to complete, the Oxford English Dictionary was about to be

Can you please explain why B is wrong and why "would take" is a better option

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thanks.

Just to clarify: we do see that you wrote "Manhattan" in the title of your thread. Believe it or not, there's another GMAT company that uses Manhattan in its name. Also, if this is one of our problems, it should be posted in the appropriately-labeled ManhattanGMAT thread (eg, MGMAT CAT, if it's a CAT problem). This is the general thread for non-ManhattanGMAT sources.

Yes -this question is from the Manhattan gmat CAT exam

B gives us two verbs in the same tense (simple past): took and was. These two events, though, clearly took place at separate points in the past, so a more complex tense is called for. (And, if we wanted to keep them both in the past tense, I would use the past perfect construction: past perfect for the first event, and simple past for the second event. But none of the answers provides this option...)

This is a very tricky question. The second clause is written as though from the viewpoint of 1860, right after the launch of the effort. From that viewpoint, the completion is still in the future (though it is in the past from today's point of view, so we use "would" instead of "will"). You aren't expected to know, inherently, that you should be talking about the completion from the "1860 point of view" - but you don't have any other options that could be correct. This is the only one that could work.