Option (B) Volcanoes is the correct answer. According to the textbook context, volcanoes bring out hot molten lava, dust, smoke, fire and magma from the volcanic crater. This material originates from the interior of the earth and can be directly observed and analyzed, making volcanoes a direct source of information. In contrast, earthquake waves (seismic activity), gravitational force, and earth magnetism are indirect sources - they help scientists make estimates and inferences about the interior but do not provide actual material for direct observation. The context clearly states that 'a part of the information is obtained through direct observations and analysis of materials,' and volcanic eruptions provide such materials from the earth's interior.