Limestone caves can be spectacular structures filled with giant stalactites and stalagmites. These caves are formed when rainwater, which is a weak acid, dissolves calcite, or lime, out of limestone. Over time, the lime-laden water drips down into cracks, enlarging them into caves. Some of the lime is then redeposited to form stalactites and stalagmites. Stalactites, which grow down from cave ceilings, are formed in limestone caves when groundwater containing dissolved lime drips from the roof of the cave and leaves a thin deposit as it evaporates. Stalactites generally grow only a fraction of an inch each year, but over time a considerable number may grow to be several yards long. In cases where the supply of water is seasonal, they may actually have growth rings resembling those on tree trunks that indicate how old the stalactites are. Stalagmites are formed on the floor of a limestone cave where water containing dissolved lime has dripped either from the cave ceiling or from a stalactite above. They develop in the same way as stalactites, when water containing dissolved limestone evaporates. In some limestone caves with mature limestone development, stalactites and stalagmites grow together, creating limestone pillars that stretch from the cave floor to the cave ceiling.10. It is indicated in paragraph 1 that all of the following are part of the process of forming limestone caves EXCEPT that
(A) rainwater dissolves lime from limestone
(B) the lime-filled water seeps into breaks in the ground
(C) the lime in the water evaporates
(D) the cracks in the ground develop into caves

11. According to paragraph 2, it is NOT true that stalactites
(A) enlarge cave ceilings
(B) are found in limestone caves
(C) grow in a downward direction
(D) grow quite slowly

12. It is NOT mentioned in paragraph 2
(A) how long stalactites may grow
(B) how the age of the stalactite is determined
(C) what one of the effects of a limited water supply is
(D) what causes stalactites to disappear

13. According to paragraph 3, stalagmites are NOT formed
(A) on cave floors
(B) from lime dissolved in water
(C) above stalactites
(D) as water containing lime evaporates

14. It is NOT indicated in paragraph 3 that limestone pillars
(A) result when a stalactite and a stalagmite grow together
(B) are attached to both the floor and the ceiling of a cave
(C) are relatively aged limestone formations
(D) are more durable than stalactites and stalagmites


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