sudarshan22Please extend the underline to the word "signify" in the question.
Meaning :
K Protocol, x & y, signify the coperation of authors;
Evaluate the setence:
S-V error - Signifies
X & Y - should be parallel.
A) and important as a vehicle by which to gain international consensus on stabilizing greenhouse gas emissions as well
S-V error
(B) and important as an important vehicle for gaining international consensus on stabilizing greenhouse gas emissions, signifies
Looks error free
(C) and also a vehicle of gaining important international consensus on the stabilization of greenhouse emissions is signifying
and + also - error
(D) an important vehicle in international consensus on stabilizing greenhouse gas emissions and have signified
Have signified - S-V error
(E) and as international consensus important to stabilizing greenhouse gas emissions too, signifies
as (an) int. consensus - as missing
to + verbing - suspect
So B wins