Critical Reasoning

Determining the authenticity of purported pre-Columbian artifacts is never easy. Carbon-14 dating of these artifacts is often impossible due to contamination by radioactive palladium (which occurs naturally in the soils of Central and South America). However, historians and anthropologists have evolved two reliable criteria, which, utilized in combination, have proven effective for dating these artifacts. First, because authentic pre-Columbian artifacts characteristically occur in a coarse, granular matrix that is shifted by major earthquakes, they often exhibit the unique scratch patterns known as gridding. In addition, true pre-Columbian artifacts show a darkening in surface color that is caused by centuries of exposure to the minute amounts of magnesium in the soil of the Americas.

The criteria above would be LEAST useful in judging the authenticity of which of the following?

(A) An ax head of black obsidian, unearthed from a kitchen midden
(B) A pottery bowl with a red ocher design, found in the ruins of a temple
(C) A set of gold ear weights, ornamented with jasper pendants
(D) A black feather cape from a king's burial vault
(E) A multicolored woven sash found near the gravesite of a slave

[spoiler]Is this GMAT Question? How to eliminate C and E?[/spoiler]
OA - D