[单项选择]The Earth comprises three principal layers: the dense, iron-rich core, the mantle made of silicate (硅酸盐) that are semi-molten at depth, and the thin, solid-surface crust. There are two kinds of crust, a lower and denser oceanic crust and an upper, lighter continental crust found over only about 40 percent of the Earth’s surface. The rocks of the crust are of very different ages. Some continental rocks are over 3,000 million years old, while those of the ocean floor are less than 200 million years old. The crusts and the top, solid part of the mantle, totaling about 70 to 100 kilometers in thickness, at present appear to consist of about 15 rigid plates, 7 of which are very large. These plates move over the semi-molten lower mantle to produce all of the major topographical (地形学的) features of the Earth. Active zones where intense deformation occurs are confined to the narrow, interconnecting boundaries of contact of the plates.
There are three main types of zones o
A. spreading contacts
B. the influence of volcanic eruptions
C. converging contacts
D. transform contacts

[单项选择]The Earth comprises three principal layers: the dense, iron-rich core, the mantle made of silicate (硅酸盐) that are semi-molten at depth, and the thin, solid-surface crust. There are two kinds of crust, a lower and denser oceanic crust and an upper, lighter continental crust found over only about 40 percent of the Earth’s surface. The rocks of the crust are of very different ages. Some continental rocks are over 3,000 million years old, while those of the ocean floor are less than 200 million years old. The crusts and the top, solid part of the mantle, totaling about 70 to 100 kilometers in thickness, at present appear to consist of about 15 rigid plates, 7 of which are very large. These plates move over the semi-molten lower mantle to produce all of the major topographical (地形学的) features of the Earth. Active zones where intense deformation occurs are confined to the narrow, interconnecting boundaries of contact of the plates.
There are three main types of zones o
A. can be classified into two types
B. is formed along the margins of the plates
C. consists of semi-molten rocks
D. is about 70 to 100 kilometers thick

[单项选择]

Nearly three-quarter of the Earth is covered with water. The (1) of the continents, especially in the temperate zones, is very much (2) by the oceans around them. The areas (3) the sea have a " (4) climate", with rather cool summers and warm winters. The interiors, far from the sea, have a climate with extremely hot summers and cold winters.
Rain comes from the evaporation of rivers, seas and lakes. (5) after heavy rain, the pavements in a city do not take (6) to dry because the rainwater evaporates into the air. On a warm dry day it evaporates very rapidly, as warm air can absorb more (7) than cold air. (8) at any particular temperature, the atmosphere can hold only a certain (9) amount of water vapor. The air is then saturated, (10) a sponge that cannot hold any more water. The lower the temperature, the (11) water vapour is required to saturate the air.
All
A. time
B. long
C. form
D. cold