Please underline the part of the sentence to be corrected.

A prolific architect who worked from the turn of the century until the late 1950's,
Julia Morgan designed nearly 800 buildings in California, perhaps most notably
William Randolph Hearst's monumental estate at San Simeon.
(A) Julia Morgan designed nearly 800 buildings in California, perhaps most
notably William Randolph Hearst's monumental estate at San Simeon
(B) perhaps the most notable of the nearly 800 buildings in California designedby Julia Morgan was William Randolph Hearst's monumental estate at San
Simeon
(C) of the nearly 800 buildings in California designed by Julia Morgan, perhaps
the most notable was William Randolph Hearst's monumental estate at San
Simeon
(D) nearly 800 buildings in California were designed by Julia Morgan, of which
William Randolph Hearst's monumental estate at San Simeon is perhaps the
most notable
(E) William Randolph Hearst's monumental estate at San Simeon is perhaps the
most notable of the nearly 800 buildings in California designed by Julia
Morgan

A prolific architect who worked from the turn of the century until the late 1950's-- This clause is modifying the architect so, immediately after the comma, we need the architect's name.

Among all the choices, only A is left and all others eliminated.

Therefore, A!