<em>The chance that a child from two people with sickle cell trait will have normal RBCs remains the same irrespective of the amount of oxygen in the environment.</em> From the cross:
AS x AS
AA AS AS SS
Hence, the chance of having a child with normal RBCs in both high and low-oxygen environments is 1/4 or 25%.
The chance that a child will have sickle cell disease is also 1/4 or 25%.
The possible genotypes in a Punnet's square can be seen in the attached image
D is correct. Newton's first law of motion states that an object in motion stays in motion. The orange is moving and then the tray stops making the orange move forward because of inertia. Hope this helps! ;)