Why did a U.S. military led coalition attack Iraq in 1991?A) to defend Saudi Arabia's democratically elected government from unprovoked aggression...

Of these options, the best answer is D.  Some of these
other answers are in some way related, but none of them is as correct as
D.

For example, it is clearly the case that the US was
trying to protect Saudi Arabia from unprovoked attack by Iraq.  However, it is in no way
correct to say that Saudi Arabia's government is democratically elected.  Iraq did have
a dictator, but the 1991 war was not meant to remove him and Saddam Hussein remained in
power for years afterwards.  Finally, Desert Storm was the name of the operation, so the
war could not have been launched to protect it.