Idiom usage?

[tanay-shah]

When the growth rate of Buenos Aires, Brazil, peaked earlier this century, the number of people migrating to the city each year was so large as to equal the present population of Seattle.

a) so large as to equal

b) so large that it has equaled

c) large enough that it equals

d) so large it equals

e) large enough to equal

---Please help between A and E? I marked E since it seems precise. But i read that the correct usage of so as to is
so [adjective] as to [verb], and hence it is used. But what is wrong with E? Moreover, is the usage mentioned above of "so as to" correct?
Thanks

[tim]

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