tailieunhanh - How to prepare for the toefl part 62

Another important strategy is to make 60-sec-ond telephone assignments. The TOEFL Academ¬ic Speaking Test (TAST), which is a preliminary version of the Speaking Section on the Next Gen¬eration TOEFL, is currently administered by tele¬phone. To prepare our students for this new expe¬rience, some of us are experimenting with phone-in speaking practice by using telephone answering machines to record our students when they call. | MODEL TEST 6 COMPUTER-ASSISTED TOEFL 613 Audio 43. What marked the end of the Stone Age Answer B . . . the introduction of metals was usually considered the defining event that brought an end to the Stone Age. Choice A refers to Chuck s idea not to the event that marked the end of the Stone Age. Choices C and D occurred much earlier. Audio Lecture Narrator Listen to part of a lecture in a geology class. The professor is talking about oil deposits. Most crude oil is found in underground formations called traps. In a trap the oil collects in porous rocks along with gas and water. Over time the oil moves up toward the surface of the earth through cracks and holes in the porous rock until it reaches a nonporous rock deposit that will not allow it to continue moving. The oil becomes trapped under the nonporous rock deposit. There are several different types of traps but today we will talk about the three most common ones the anticline trap the salt dome trap and the fault trap. Look at this diagram. Here is an example of an anticline. As you can see the oil is trapped under a formation of rock that resembles an arch. In this anticline the petroleum is trapped under a formation of nonporous rock with a gas deposit directly over it. This is fairly typical of an anticline. 614 EXPLANATORY ANSWERS AND AUDIO SCRIPTS Now let s look at a diagram of a salt dome. This salt dome shows how a cylinder-shaped salt deposit has pushed up through a layer of sedimentary rocks causing them to arch and fracture. The oil deposits have collected along the sides of the salt dome. Nonporous rock s Porous rocK s Finally I want to show you a fault trap. This diagram represents a fracture in the Earth that has shifted a nonporous rock formation on top of a porous formation. Remember as in all traps the oil is collected in the porous rock and trapped underground by the nonporous rock. Geologists study the terrain for indications of possible oil traps. For example a bulge in a flat surface may .