Answer:
The sentece that used Hyphen correctly is:
A. Emma claimed responsibility for the well-placed American flag.
Explanation:
To understand this answer we need to analyze all of them.
a) This is the correct answer because we have a noun modifying an act to create a new concept.
b) in this case the hyphen is not necessary because so is used to emphasize not to unite two concepts to create another one.
c) In this case, it is also unnecessary because the meaning of the concept can be understood without the hyphen.
d) In this case, it is unnecessary because as in case c) the meaning can be understood without the hyphen, therefore we don't need it.
