Directions: Read the passage. Then answer the questions.
Photographic evidence suggests that liquid water once existed in great quantity
on the surface of Mars. Two types of flow features are seen: runoff channels and
outflow channels. Runoff channels are found in the southern highlands. These flow
features are extensive systems—sometimes hundreds of kilometers in total length—of
interconnecting, twisting channels that seem to merge into larger, wider channels.
They bear a strong resemblance to river systems on Earth, and geologists think that
they are dried-up beds of long-gone rivers that once carried rainfall on Mars from the
mountains down into the valleys. Runoff channels on Mars speak of a time 4 billion
years ago (the age of the Martian highlands), when the atmosphere was thicker, the
surface warmer, and liquid water widespread.
Directions: Now answer the questions.
1. The word “merge” in the passage is closest in meaning to
(C) straighten out
2. What does the discussion in paragraph 1 of runoff channels in the southern highlands suggest
(A) The atmosphere of Mars was once thinner than it is today.
(B) Large amounts of rain once fell on parts of Mars.
(C) The river systems of Mars were once more extensive than Earth’s. (D) The rivers of Mars began to dry up about 4 billion years ago.