Sentence Correction

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

OA: D

Please explain..

would - conditional tense usage.Hence a future can be envisioned in past 'sense'.
Hence, the action - project taking more than 60 years to complete uses 'Would'.
POE B,E.

was Being - being is redundant usage of to be verb here.POE C.

between A and D :
Had been - makes the 'birth' action further in the past than the process of 60 years for the project.Wrong usage. POE A.

D uses the correct verb Was here. hence OA.