Which Statement Describes a Primary Mutant Screen

Which statement describes a primary mutant screen?

A) A researcher uses CRISPR to create mutations in mouse homologs of three genes that function in heart development in the fruit fly.
B) A scientist uses RNAi to simultaneously knock down the expression of two genes in C.elegans to determine whether they function redundantly.
C) A scientist examines a large number of mutagenized zebrafish embryos for abnormalities in blood vessel formation.
D) A researcher treats a large number of Arabidopsis plants with different chemicals to determine which chemicals inhibit plant growth.