LSAT Assumption qstn- effective way to reduce such emissions

Please hlep me with your response on below CR Assumption question from LSAT powerScore CR guide:

Emissions from automobiles that burn gasoline and
automobiles that burn diesel fuel are threatening the
quality of life on our planet, contaminating both
urban air and global atmosphere. Therefore, the only
effective way to reduce such emissions is to replace
the conventional diesel fuel and gasoline used in
automobiles with cleaner-burning fuels, such as
methanol, that create fewer emissions.
Which one of the following is an assumption on
which the argument depends?
(A) Reducing the use of automobiles would not
be a more effective means to reduce
automobile emissions than the use of
methanol.
(B) There is no fuel other than methanol that is
cleaner-burning than both diesel fuel and
gasoline.
(C) If given a choice of automobile fuels,
automobile owners would not select
gasoline over methanol.
(D) Automobile emissions constitute the most
serious threat to the global environment.
(E) At any given time there is a direct correlation
between the level of urban air pollution and
the level of contamination present in the
global atmosphere.
OA follows..