Certain environmental conditions increase the occurrence of diseases. A polluted environment in terms of air pollution poses risk of developing respiratory disease such as asthma in allergic individuals or in the individuals with hyperactive immune system. Likewise, individuals with defective melanin production gene are more likely to develop skin cancer upon exposure to UV lights. Hence, specific conditions stimulate disease occurrence.
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! ;)