第4段的crude和以下哪个词意思最相近。
第4段开始写到,researchers将“directed aerial descent”这个能力用在没有明显空气动力能力,但是却运用一种非常基础,没有效率,但是比较有用的滑翔的动物身上。crude在这里的意思是marked by the primitive, gross, or elemental or by uncultivated simplicity,对应B basic。
A obvious: easily discovered, seen, or understood 明显的
C offensive: making attack : AGGRESSIVE 冒犯的
D obsolete(这个词是高频词汇): not in use any more, having been replaced by something newer and better or more fashionable 废弃的