○Ancient

4、According to paragraphs 1 and 2, which of the following is NOT true of the shield volcanoes on the Tharsis bulge?

They have broad, sloping sides.

They are smaller than the largest volcano on Mars.

They have channels that resemble the lava channels of volcanoes on Earth.

They are over 25 kilometers tall.

Paragraph 3

The great height of Martian volcanoes is a direct consequence of the planet's low surface gravity. As lava flows and spreads to form a shield volcano, the volcano's eventual height depends on the new mountain's ability to support its own weight. The lower the gravity, the lesser the weight and the greater the height of the mountain. It is no accident that Maxwell Mons on Venus and the Hawaiian shield volcanoes on Earth rise to about the same height (about 10 kilometers) above their respective bases-Earth and Venus have similar surface gravity. Mars's surface gravity is only 40 percent that of Earth, so volcanoes rise roughly 2.5 times as high. Are the Martian shield volcanoes still active? Scientists have no direct evidence for recent or ongoing eruptions, but if these volcanoes were active as recently as 100 million, years ago (an estimate of the time of last "eruption based on the extent of impact cratering on their slopes), some of them may still be at least intermittently active. Millions of years, though, may pass between eruptions.

5、The word "roughly" closest In meaning to

Typically

Frequently

Actually

Approximately

6、In paragraph 3, why does the author compare Maxwell Mons on Venus to the Hawaiian shield volcanoes on Earth?

To help explain the relationship between surface gravity and volcano height

To explain why Mars's surface gravity is only 40 percent of Earth's

To point out differences between the surface gravity of Earth and the surface gravity of Venus

To argue that there are more similarities than differences between volcanoes on different planets

7、 Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

Although direct evidence of recent eruptions is lacking, scientists believe that these volcanoes were active as recently as 100 million years ago.

Scientists estimate that volcanoes active more recently than 100 years ago will still have extensive impact cratering on their slopes.

If, as some evidence suggests, these volcanoes erupted as recently as 100 million years ago, they may continue to be intermittently active.

Although these volcanoes were active as recently as 100 million years ago, there is no direct evidence of recent or ongoing eruptions.

Paragraph 4

Another prominent feature of Mars's surface is cratering. The Mariner spacecraft found that the surface of Mars, as well as that of its two moons, is pitted with impact craters formed by meteoroids falling in from space. As on our Moon, the smaller craters are often filled with surface matter-mostly dust-confirming that Mars is a dry desert world. However, Martian craters get filled in considerably faster than their lunar counterparts. On the Moon, ancient craters less than 100 meters across (corresponding to depths of about 20 meters) have been obliterated, primarily by meteoritic erosion. On Mars, there are relatively few craters less than 5 kilometers in diameter. The Martian atmosphere is an efficient erosive agent, with Martian winds transporting dust from place to place and erasing surface features much faster than meteoritic impacts alone can obliterate them.