Smooth muscle cells are found in the walls of hollow organs
I think the correct answer from the choices listed above is the second option. The enzyme pepsin that is present in the stomach denature in the intestine due to the alkaline environment of the intestine. This is because pepsin has an optimum pH that is very low which is ideal for the acidic conditions of the stomach.
Because the three-horned alien is heterozygous, we know that three must be dominant to four, because the gene for the three horns is "hiding" the gene for four horns. Therefore, the three-horned alien has the genotype Tt (T for three horns, and t for four horns). The four horned alien must be tt, because that is the only way that a recessive trait may be seen. If you solve the punnet square on a cross between Tt and tt, you end up with half three (heterozygous) and half four (homozygous recessive) it is a bit easier to explain with something a little "closer to home" if you want me to explain it again, just say so, I don't mind!