The correct answer is D. no article.
Newer planes are generally safer than older planes because they have more advanced safety features and are built with newer technology. For example, newer planes may have better engines, which are less likely to fail. They may also have better avionics, which can help pilots avoid dangerous situations. Additionally, newer planes are often subject to more rigorous safety inspections than older planes.
The article “a” is used before singular nouns that refer to a specific person, place, thing, or idea. In this case, the noun “plane” is not specific, so the article “a” is not necessary.
The article “an” is used before singular nouns that begin with a vowel sound. In this case, the noun “plane” does not begin with a vowel sound, so the article “an” is not necessary.
The article “the” is used before singular nouns that refer to a specific person, place, thing, or idea that has already been mentioned. In this case, the noun “plane” is not specific, so the article “the” is not necessary.