They may have other language goals as well, such as learn¬ing to communicate more effectively or improving their writing, but these goals do not usually exert the same kinds of pressure that the required TOEFL score does. | MODEL TEST 4 COMPUTER-ASSISTED TOEFL 573 Audio 41. When would the man be available Answer D . when could you start Right away Choices A and B are not correct because he will complete his dissertation after work and on his days off and he will graduate after the dissertation is complete. Choice C refers to when he will write his dissertation not to when he will be available for work. Audio Lecture Narrator Listen to part of a lecture on solar heating. In general solar heating requires a solar collector a water or air distribution system and a storage system. Most of the time a solar collector is mounted on the roof of a building at a somewhat steep angle positioned with a southern exposure. In the hot water system that I am going to show you the collector is a glass plate with another plate under it and an air space between the two through which water can be pumped. I think it will make more sense when you see the model so let s look at it now. Notice that water that has been heated by the sun is pumped in closely positioned tubes through the space between the plates. The hot water is then pumped to a storage tank and warmed air is circulated to the other side of the building with a fan. You will also see a backup heater in this system usually a conventional furnace because only about 20 to 30 percent of the solar energy can actually be used in this design. The supply air moves across the space to be heated and enters the return air exchanger where it rises and with exposure to the sun begins heating again to raise the temperature of the water in the tubes below. So the process begins again. Of course one of the problems with solar heat is the intermittent nature of solar radiation as an energy source. Especially in climates where the sun does not shine regularly it just isn t a feasible option without large and often complex storage systems. However scientists are now working on a project to place solar modules in orbit around the Earth where energy generated by .
