The correct answer is C. are unconstitutional if drawn based on race alone.
In 2015, Majority-minority districts represented approximately 28% of the Congressional districts in the United States (122 of the nation's 435 house districts.
In 2017, in Court v. Harris, the Supreme Court ruled that the mapping of Districts 1 and 12 in the North Carolina's Congressional map was unconstitutional because it was drawn based on race alone. This practice is called racial gerrymandering.