Read the following passage and choose the best answer to each question. Write your answers in the space provided.
For centuries, skywatchers have reported seeing mysterious flashes of light on the surface of the Moon. Modern astronomers have observed the same phenomenon, but no one has been able to satisfactorily explain how or why the sporadically sparks. However, researchers now believe they have found the cause.
Researchers have explained the chemical content of Moon rocks retrieved by astronauts during the Apollo missions and have found that they contain volatile gases such as helium, hydrogen, and argon. The researchers suggest that stray electrons, freed when the rock cracks, may ignite these gases. Indeed, lunar rock samples, when fractured in the lab, throw off sparks.
What causes these rocks to crack to the lunar surface? The flashes are most often seen at the borders between sunlight and on the Moon, where the surface is being either intensively heated or cooled. A sudden temperature change may cause thermal cracking. Another possibility is that meteors may strike the rocks and cause them to crack. Finally, lunar rocks may be fractured by seismic events- in other words, by tiny moonquakes.
According to the passage, the theory that Moon rocks give off sparks when they crack is supported by…………………………
