Definition: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Input: Passage: Two young American couples — Jeff and Amy, and Eric and Stacy — enjoy their vacation in Mexico. They meet Mathias, a German tourist, who is looking for his brother Heinrich. His last known location is an archaeological dig at a remote Mayan ruin in the jungle. They are also joined by Dimitri, Mathias's friend. The group reaches the ruins of a Mayan temple, and are confronted by Mayan villagers with guns and bows. Mathias tries to explain their purpose, but the villagers do not understand Spanish or English. When Amy accidentally touches some vines the villagers become increasingly agitated. Dimitri approaches the villagers, hoping to appease them, but they shoot and kill him. The rest of the group flees up the steps of the ruins.
At the top, they find an abandoned camp and a shaft in the center. The group cannot call for help since Eric's phone has no signal. They hear a cell phone ringing from somewhere inside the ruins. Believing it is Heinrich's phone ringing, the rest of the group lowers Mathias down the shaft with a rope. The rope breaks and Mathias falls, becoming completely paralyzed. Amy and Jeff descend the temple steps hoping to reason with the Mayans, but to no success. In anger, Amy throws a clump of vines at them and hits a young boy, whom the Mayans promptly kill. They realize the Mayans are afraid of the vines, and won't let them go since they have touched them. Later, Stacy and Amy descend the shaft to help Mathias and to find the phone. Jeff and Eric rig a backboard and bring Mathias out of the shaft.

What are the first names of the people that go to the Mayan Temple?