The (initial discovery) by humans almost 10000 years ago that they could exploit (metallic mineral) deposits was (an important) milestone in the (development civilization).
答案选D 不明白错哪里了.
The (taller) of all animals, a (full-grown) giraffe (may be) eighteen feet or more (heigh).
答案选A,但D,more heigh有这种用法吗?