1. The word "modifying" in line 4 is closest in meaning to
(A) changing
(B) traveling
(C) describing
(D) destroying

47.The author mentions the extinction of the dinosaurs in the second paragraph to emphasize that (A)the cause of the dinosaurs extinction is unknown (B)Earth's climate has changed significantly since the dinosaurs' extinction, (C)not all mass extinctions have been caused by human activity (D) actions by humans could not stop the irreversible process of a species' extinction

48.The word "magnitude" in line 20 is closest in meaning to (A) concern (B) determination (C)carelessness (D) extent

49. According to the passage, natural evolutionary change is different from changes caused by humans in that changes caused by humans (A) are occurring at a much faster rate (B) are less devastating to most species (C)affect fewer ecosystems (D) are reversible

50. With which of the following statements would the author be most likely to agree? (A)human influence on ecosystems should not be a factor in determining public policy. (B)The extinction of a few species is an acceptable consequence of human progress. (C)Technology will provide solutions to problems caused by the destruction of ecosystems. (D) humans should be more conscious of the influence they have on ecosystems

2. The word "which" in line 5 refers to (A) clouds (B) oceans (C) continents (D) compounds

3. According to the passage, clouds are primarily formed by water (A) precipitating onto the ground (B) changing from a solid to a liquid state (C) evaporating from the oceans (D) being carried by wind

4. The passage suggests that the purpose of the "hydrographic network" (line 9) is to (A) determine the size of molecules of water (B) prevent soil erosion caused by flooding (C) move water from the Earth's surface to the oceans (D) regulate the rate of water flow from streams and rivers

5. What determines the rate at which a molecule of water moves through the cycle, as discussed in the third paragraph? (A) The potential energy contained in water (B) The effects of atmospheric pressure on chemical compounds (C) The amounts of rainfall that fall on the continents (D) The relative size of the water storage areas

6. The word "rapidity" in line 19 is closest in meaning to (A) significance (B) method (C) swiftness (D) reliability

7. The word "they" in line 24 refers to (A) insoluble ions (B) soluble ions (C) soils (D) continents