Which of the Following Is True

Which of the following is true?

A) GWAS is able to determine a single gene that plays the sole role in the development of Crohn's disease.
B) GWAS requires controlled crosses and the formation of introgression lines.
C) QTL mapping approaches can analyze organisms in random mating populations.
D) GWAS can scan the entire genome for QTLs by statistically testing for marker variants.
E) QTL mapping can directly identify the gene responsible for the associated phenotypic variation.