Based on the information present in the given passage, you need to write a correct answer to the given question. A correct answer is one that correctly and completely answers the question. Do not write answers that address the question partially or incorrectly. The correct answer must be contained in the given paragraph.
One example: Paragraph- Sent 1: Obama was born on August 4, 1961, at Kapiʻolani Maternity & Gynecological Hospital in Honolulu, Hawaii.
Sent 2: He is the only President to have been born in Hawaii.
Sent 3: He was born to a white mother and a black father.
Sent 4: His mother, Ann Dunham (1942-1995), was born in Wichita, Kansas, of mostly English descent, with some German, Irish, Scottish, Swiss, and Welsh ancestry. Question: How old was Obama's mother when he was born?
Solution is here: 19.
Explanation: Obama was born in 1961. His mother was born in 1942 and 1961-1942=19. Therefore, any of the following responses are considred correct: '19' and 'almost twenty'.

Now, solve this: Paragraph- Sent 1: The inhabited history of the Las Vegas Valley stretches to 23,000 b.c.
Sent 2: , when much of the area was covered by a prehistoric lake.
Sent 3: During this period, the indigenous people lived in caves, hunting the mammals that gathered at the shoreline.
Sent 4: The landscape of the valley changed dramatically over the next 200 centuries.
Sent 5: The glaciers feeding the lake melted away and the lake evaporated.
Sent 6: Fossils tell an obscure story of man's slow and sporadic development.
Sent 7: Around 3000 b.c.
Sent 8: , native Archaic Indians began to develop a lasting hunting and gathering culture.
Sent 9: By this time, the valley was in much the same geographic state as it exists in today, with one exception — the presence of artesian springs that bubbled to the surface in several areas.
Sent 10: These springs fed a network of streams draining through the Las Vegas Wash to the Colorado River.
Sent 11: The areas surrounding the springs were desert oases: sprawling collections of grasses, trees, and wildlife.
Sent 12: Many springs lay in areas that would eventually become the center of the modern Las Vegas metropolis.
Sent 13: For about 4000 years, the Archaics thrived in a culture that included many signs of early civilization.
Sent 14: Signs of even more advancement appeared halfway through the first millennium a.d.
Sent 15: , when the Anasazi Indians inhabited the valley.
Sent 16: Far more progressive than the Archaics, the Anasazi utilized such formal agricultural techniques as irrigation to assist their harvest.
Sent 17: This permitted the Anasazi to achieve a benchmark of advanced society — the ability to live in permanent shelters year-round without need to follow wildlife.
Sent 18: Mysteriously, the Anasazi vanished from the valley around a.d. 
Question: Who was the most advance early civilization that disappeared in Las Vegas?.
Solution:
The Anasazi.