Main Idea Practice Test

Read the passage, then answer the question.

When scientists first began studying glaciers closely, they noticed that these massive rivers of ice are not motionless. A glacier may appear frozen in place, but it slowly flows downhill under its own weight. This movement can reshape the land. As ice drags rocks along, it scrapes valleys, grinds stone into fine sediment, and carries debris for long distances.

Glaciers also store fresh water. In many regions, meltwater from glaciers feeds rivers during warmer months. Communities rely on this water for drinking, farming, and generating electricity. Because of this, changes in glacier size can affect people far from the ice itself.

In recent decades, many glaciers have been shrinking. Warmer temperatures cause more melting, and some glaciers receive less snowfall to replace lost ice. Scientists measure these changes using photographs, field studies, and satellite data. The shrinking of glaciers can lead to higher sea levels and can reduce the steady summer water supply that some areas depend on.

The passage emphasizes that glaciers matter because they shape landscapes and support human needs. Understanding how glaciers move and change helps communities plan for the future and manage water resources wisely.

What is the central theme presented in the text?

Read the passage, then answer the question.

In ancient times, many people measured time by watching the sun. Sundials could show the hour on a clear day, but they failed at night or during cloudy weather. As societies grew more complex, accurate timekeeping became more important. Farmers wanted to plan work, religious communities needed regular schedules, and cities depended on coordinated activities.

Mechanical clocks began to appear in Europe during the Middle Ages. Early versions were large and often placed in towers where many people could see and hear them. These clocks used gears and weights to keep time, and they rang bells to mark hours. While they were not perfectly accurate at first, they offered something new: time that did not depend on sunshine.

Over centuries, clockmakers improved their designs. Springs replaced some weights, allowing smaller clocks that could fit inside homes. Better materials reduced friction, and careful craftsmanship made clocks more reliable. As clocks spread, they changed daily habits. People began to schedule meetings more precisely and to think of time as something that could be “spent” or “saved.”

The passage suggests that mechanical clocks did more than tell time. They helped shape a new way of organizing society. By making time measurable in a consistent way, clocks influenced work, travel, and even how people understood responsibility and punctuality.

Which statement best captures the main idea of the passage?