I disagree with one of the answers, and I’d like someone to explain further: Question 6:
According to paragraph 4, what has recent research on obsidian tools found at Olmec sites shown?
A. Obsidian’s value was understood only when Teotihuacán became an important city.
B. The residents of Teotihuacán were sophisticated toolmakers.
C. The residents of Teotihuacán traded obsidian with the Olmecs as early as 400 B.C.
D. Some of the obsidian used by the Olmecs came from the area around Teotihuacán.
The paragraph clearly says “Teotihuacán obsidian must have been recognized as a valuable commodity for many centuries before the great city arose” eliminating option A.
And it also says : "recent research on obsidian tools found at Olmec sites has shown that some of the obsidian obtained by the Olmecs originated near Teotihuacán"
In my opinion, confirming option D.
Please explain how I’m wrong.