You are given a paragraph, a question and some answer options (associated with "A", "B", "C", "D", etc.) You need to list all the correct answer options with their associated letters (e.g. "A" can be a valid answer). Note that sometimes, more than one option can answer the question correctly and completely. In those cases, please generate all such options separated by a comma (e.g. "A, B" is a valid answer). Do not generate anything else apart from one or more of the following characters: 'A', 'B, 'C', 'D', etc.

[EX Q]: 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 exceptionthe 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 societythe 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: Approximately what year was the Las Vegas Valley covered by a prehistoric lake? (A) 23,000 b.c (B) 1500 b.c (C) Around 3000 b.c (D) 2000 b.c.
[EX A]: A.

[EX Q]: Paragraph- Sent 1: Abrasion is another type of weathering.
Sent 2: Like ice wedging, it is a form of mechanical weathering.
Sent 3: Like ice wedging, abrasion does not change the rock into another type of rock.
Sent 4: With abrasion, one rock or piece of sediment bumps against another rock.
Sent 5: Rocks dont normally roll around on their own, so why do they move?
Sent 6: There are a couple of reasons a rock may move.
Sent 7: Gravity can cause rocks to move.
Sent 8: They may roll downhill or fall off a cliff.
Sent 9: As they roll down a hill, they bump into each other.
Sent 10: Maybe a moving rock hits a rock that is not moving at the bottom of the hill.
Sent 11: Moving water causes rocks and sediment to move.
Sent 12: Rocks are bounced along the bottom and bump against one another.
Sent 13: As they collide, they begin to chip away at each other.
Sent 14: Angular rocks become more rounded with each collision.
Sent 15: Strong winds cause abrasion.
Sent 16: The wind carries sediment.
Sent 17: This sediment is thrown against other rocky surfaces by the wind.
Sent 18: It is like sand-blasting a rock.
Question: How does gravity cause rocks to move? (A) With water force (B) They bump into each other (C) With a push and pull (D) They may roll downhill (E) They may fall off a cliff (F) With kinetic force (G) They may roll downhill or fall off a cliff.
[EX A]: D, E, G.

[EX Q]: Paragraph- Sent 1: Earth processes have not changed over time.
Sent 2: The way things happen now is the same way things happened in the past.
Sent 3: Mountains grow and mountains slowly wear away.
Sent 4: The same process is at work the same as it was billions of years ago.
Sent 5: As the environment changes, living creatures adapt.
Sent 6: They change over time.
Sent 7: Some organisms may not be able to adapt.
Sent 8: They become extinct.
Sent 9: Becoming extinct means they die out completely.
Sent 10: Some geologists study the history of the Earth.
Sent 11: They want to learn about Earths past.
Sent 12: They use clues from rocks and fossils.
Sent 13: They use these clues to make sense of events.
Sent 14: The goal is to place things in the order they happened.
Sent 15: They also want to know how long it took for those events to happen.
Question: According to this passage, on what planet do mountains grow and wear away? (A) Some organisms (B) Mars (C) The Earth.
[EX A]:
C.