A volcano is an opening in the earth’s surface through (23)___________ lava, hot, gases and rock fragments erupt. (24) ________ an opening occurs when melted rock from deep within the earth blasts through the surface. Most volcanoes are a top mountains, particularly cone-shaped mountains. The mountains themselves are also called volcanoes. Eruptions of volcanic mountains are spectacular sights. In some eruptions, huge fiery clouds rise over the mountain, and growing rivers of lava flow down (25) _________ sides. In other eruptions, red- hot ash and cinders shoot out the mountaintop, and large chunks of hot rockare blasted (26) ________ into the air. A few eruptions are so ( 27) _________ that they blow the mountain apart. Some eruptions occur on volcanic islands. Such islands are the tops of volcanic mountains that have been built (28) __________ from the ocean floor by repeated eruptions. Other eruptions occur along narrow cracks in the ocean floor. 23/ A. which B. that C. where D. when 24/ A. So B. Such C. That D. Many 25/ A. its B. it C. their D. theirs 26/ A. high B. low C. below D. above 27/ A. gentle B. violent C. terrible D. awful 28/ A. up B. on C. into D. onto