20. The primary purpose of the passage is to
(A) describe the way in which hot spots influence the extinction of volcanoes
(B) describe and explain the formation of the oceans and continents
(C) explain how to estimate the age of lava flows from extinct volcanoes
(D) describe hot spots and explain how they appear to influence and record the motion of plates
(E) describe the formation and orientation of island chains in the Pacific Ocean
21. According to the passage, hot spots differ from most volcanoes in that hot spots
(A) can only be found near islands
(B) are active whereas all other volcanoes are extinct
(C) are situated closer to the earth's surface
(D) can be found along the edges of the plates
(E) have greater amounts of alkali metals in their lavas
22. It can be inferred from the passage that evidence for the apparent course of the Pacific plate has been provided by the
(A) contours of the continents.
(B) dimensions of ocean hot spots
(C) concurrent movement of two hot spots
(D) pattern of fissures in the ocean floor
(E) configurations of several mid-ocean island chains
23. It can be inferred from the passage that the spreading out of lavas of different ages at hot spots indicates that a
(A) hot spot is active
(B) continental plate has moved
(C) continental rupture is imminent
(D) hot spot had been moving very rapidly
(E) volcano contains large concentrations of alkali metals
24. The passage suggests which of the following about the Hawaiian Islands, the Austral Ridge, and the Tuamotu Ridge?
(A) The three chains of islands are moving east- ward.
(B) All the islands in the three chains have stopped moving.
(C) The three islands chains are a result of the same plate movement.
(D) The Hawaiian Islands are receding from the other two island chains at a relatively rapid rate.
(E) The Austral Ridge and the Tuamotu Ridge chains have moved closer together whereas the Hawaiian Islands have remained stationary.
25. Which of the following, if true, would best support the author's statement that hot-spot activity may explain the mutability of continental plates?
(A) Hot spots move more rapidly than the continental and oceanic plates.
(B) Hot spots are reliable indicators of the age of continental plates.
(C) Hot spots are regions of volcanic activity found only in the interiors of the continental plates.
(D) The alignment of hot spots in the Pacific. Ocean parallels the alignment of Pacific Ocean islands.
(E) The coastlines of Africa and South America suggest that they may once have constituted a single continent that ruptured along a line of hot spots.
26. The author's argument that hot spots can be used to reconstruct the movement of continental plates is weakened by the fact that
(A) hot spots are never found at the boundaries of plates
(B) only extinct volcanoes remain after a plate moves over a hot spot
(C) lava flow patterns for all hot spots have not been shown to be the same
(D) the immobility or near immobility of hot spots has not been conclusively proven
(E) the changing configurations of islands make pinpointing the locations of hot spots difficult
27. The author's style can best be described as
(A) dramatic
(B) archaic
(C)esoteric
(D) objective
(E) humanistic
28. SUBTLE:
(A) careful
(B) dirty
(C) obvious
(D) intentional
(E) eager
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