1. Which of the following sentences does NOT employ correct word usage?

a. We had to travel several miles further into the Arkansas Ozarks to locate the Buffalo River.
b. Because this river is only 130 miles long, many people are surprised that it has been designated the first national river in the U.S.
c. Southerners whoa re enthusiastic about outdoor recreation aren't surprised by the recognition because they have known about the Buffalo River for many years.
d. Fewer boats traveled down this white water before its designation as a national river.

I think it's D?

Nope. D is o.k.

For C I meant who are* , C doesn't sound right?

We can't always depend upon what sounds "right."

One of the sentences has misused a word.

http://englishplus.com/grammar/00000213.htm

Okay, thanks I understand the mistake now.

To determine which sentence does NOT employ correct word usage, let's analyze each option:

a. "We had to travel several miles further into the Arkansas Ozarks to locate the Buffalo River."
This sentence is grammatically correct and uses the comparative form of the adverb "further" correctly to compare the distance traveled.

b. "Because this river is only 130 miles long, many people are surprised that it has been designated the first national river in the U.S."
This sentence is also grammatically correct and uses the word "first" correctly to describe the Buffalo River as being the first national river in the U.S.

c. "Southerners whoa re enthusiastic about outdoor recreation aren't surprised by the recognition because they have known about the Buffalo River for many years."
This sentence is grammatically correct, with the minor typo of "whoa" instead of "who," but that does not affect the word usage in the question.

d. "Fewer boats traveled down this white water before its designation as a national river."
This sentence employs incorrect word usage. The phrase "this white water" is not accurately describing the Buffalo River. It would be more appropriate to say "this whitewater river" or "this white-water stretch."

Therefore, your intuition is correct. The sentence that does NOT employ correct word usage is option (d), "Fewer boats traveled down this white water before its designation as a national river."