Which was the first to decrease?
a) number of american troops in vietnam
b) north vietnamese willingness to accept casualties
c) number of bombing missions against the north
d) domestic support for the war in the us

from this list of options, the first to decrease was "number of bombing missions against the north". this was followed by domestic support for the war and then troop levels.

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explanation:

the answer to your question is a. the salt plains

in 1811, he led an expedition, known as the george c. sibley expedition, to improve relations with the pawnee and kansa tribes, and also to locate the rumored jefferson's salt mountain