更多"Radiocarbon Dating
Nowadays scie"的相关试题:
[单项选择] Radiocarbon Dating
Nowadays scientists can answer many questions about the past through a technique called radiocarbon (放射性碳), or carbon-14, dating. One key to understanding how and by something happened is to discover when it happened.
Radiocarbon dating was developed in the late 1940s by physicist Willard F. Libby at he 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 he 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 samp
A. Right
B. Wrong
C. Not mentioned
[单项选择]Nowadays, we can purchase things on-line（ ）.
A. read
B. buy
C. rent
D. watch
[填空题]Nowadays, companies can______(充分利用众多的媒体对产品进行广告宣传) so as to boost their sales.
[多项选择]Directions:
Nowadays we can see American films and TV programs pouring in, fast food restaurants popping up in our cities, and many other imported products dominating our markets. Many people are happy to see them whereas others worry about such trends. Give your opinion in an essay of no less than 250 words.
[多项选择]Nowadays we can see American films and TV programs pouring in,fast food res taurants popping up in our cities, and many other imported products dominating our markets. Many people are happy to see them whereas others worry about such trends. Give your opinion in an essay of no less than 250 words.
[填空题]Nowadays, large jet airplanes can cross America in five hours and land at______.
[填空题]
Supermarket dating, where single person can check each other
out via the contents of their baskets, flirt(调情) while weighing vegetable and
even walk down the lanes of the market together, is coming to Paris. Lafayette
Gourmet, the food hall at the Galeries Lafayette department store in Paris, is
about to unleash(释放) the{{U}} (47) {{/U}}on the worldwide capital of
romance. Single shoppers will be{{U}} (48) {{/U}}on Thursday evening by
special purple shopping baskets{{U}} (49) {{/U}}with a cartoon of a
kissing couple, and{{U}} (50) {{/U}}a glass of champagne and a free
photograph if they succeed in picking up a{{U}} (51) {{/U}}mate. "We
noticed that we have an evening client group buying single portion of{{U}}
(52) {{/U}}food, so we decided the demand is there," Lafayette Gourmet
Director Sylvain Gaudu told reporters. Paris, home to around 900,000 singles,
many of whom are{{U}} (53) {{/U}}working hours as long as in London and
New Yo
