Many scientists believe that dinosaurs became extinct due to
O floods caused by strong storms.
O a harmful genetic mutation.
O the introduction of a predator.
O an asteroid impact

an asteroid impact

Explanation:

The asteroid that formed a crater located on the edge of the Yucatan peninsula thought to be responsible for the mass extinction of dinosaurs.

"do a testcross with a homozygous recessive plant."

i think the answer is a.keratin is the pigment responsible for skin color.