填空题. When Jules Verne wrote Journey to the Center of the Earth in 1864, there were many 11 theories about the nature of the Earth's interior. Some geologists thought that it contained a highly compressed ball of glowing gas, while others suspected that it 12 of separate shells, each made of a different material. Most of our knowledge of the Earth's interior comes not from mines or boreholes, but from the study of seismic waves (震波)— powerful pulses of energy 13 by earthquakes. The way that seismic waves travel shows that the Earth's interior is far from uniform. The 14 and the seabed are formed by the crust (地壳)— a thin sphere of relatively light, solid rock. Beneath the crust lies the mantle, a very different layer that extends approximately halfway to the Earth's center. There the rock is the subject of a battle between increasing heat and 15 pressure. In its high levels, the mantle is relatively cool; at greater depths, high temperatures make the rock behave more like a liquid than a solid. Deeper still, the pressure is even more 16 , preventing the rock from melting in spite of a higher temperature. Beyond a depth of around 2,900 kilometers, a great change takes place and the mantle gives 17 to the core. Some seismic waves cannot pass through the core and others are bent by it. From this and other evidence, geologists assume that the outer core is 18 liquid, with a solid center. The conditions in the Earth's core make it a far more 19 world than space. Its solid iron heart is subjected to unimaginable pressure and has a temperature of about 9,000° F. Although scientists can 20 about its nature, neither humans nor machines will ever be able to visit it. A. way B. ponder C. alien D. iron E. growing F. harmonious G. speculate H. consisted I. intense J. exactly K. continents L. conflicting M. highway N. released O. probably