Even I chose (A) initially, but a closer look suggests that the OA is correct after all.
Compare A to D in terms of the description of the twin tower:
A: responding to the devastating attack on New York’s World Trade Center’s Twin Towers, President Bush ordered
D: in response to the devastating attack on the Twin Towers, part of New York’s World Trade Center, President Bush ordered
"NEW YORK'S WORLD TRADE CENTER'S TWIN TOWERS" ---double possessive (is it?) doesn't sound good
"TWIN TOWER, PART OF NEW YORK'S WORLD TRADE CENTER"--- better
Also look at the expression; its like saying,
A: In Oct. 2001,
responding to ABC, President Bush ordered XYZD: In Oct. 2001,
in response to ABC, President Bush ordered XYZA: President Bush acted responding to an attack- this doesn't sound better than option D
D: President Bush acted in response to an attack- better
Verbal gurus, your inputs please.