In recent years, we have seen great progress in house building. The type of houses found in a certain part of the world depends to a certain extent on the building materials available there. Countries where stone is abundant tend to have more stone houses than a place where there is plenty of timber for example. However, climatic conditions affect the houses built to a greater extent.
In equatorial countries like Singapore and Malaysia, two main factors are responsible for the type of houses built: the heat of the sun and the fierceness of rainstorms. Our houses are light and airy but have steep roofs. In some places, houses are built on stilts because they may be in lowlying areas which get flooded easily.
In a hot and dry country such as Arabia, the houses are often box-shaped. They have thick stone walls which are painted white. White surfaces radiate heat while dark surfaces absorb it. The houses have
A. are light and airy
B. have steep roofs
C. are always built on stilts
D. are built to shelter from the harsh elements
Radiocarbon Dating
Nowadays scientists can answer many questions about the past through a technique called radiocarbon (放射), or carbon-14, dating. One key to understanding how and why something happened is to discover when it happened.
Radiocarbon dating was developed in the late 1940s by physicist Willard F. Libby at the University of Chicago. An atom of ordinary carbon, called carbon-12, has six protons (质子) and six neutrons (中子) in its nucleus(原子核). Carbon-14,or C-14,is a radioactive,unstable form of carbon that has two extra neutrons. It returns to a more stable form of carbon through a process called decay(衰减). This process involves the loss of the extra neutrons and energy from the nucleus.
In Libby’s radiocarbon dating technique, the weak radioactive emissions (放射)from this decay process are counted by instruments such as a radiation detector and counter. The decay rate is used to determine the proportion of C-14 atoms in the ’sam
A. Right
B. Wrong
C. Not mentioned
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