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举例说明生色团和助色团。

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为什么原子光谱呈线状光谱，而分子光谱呈带状光谱？

Directions: Now, you will hear three news reports. At the end of each news report, youwill hear two or three questions. Both the news report and the questions will be spoken only once. After you hear a question, you are supposed to choose the best answer from the four choices marked A), B),C) and D).Questions 1 and 2 will be based on News ltem 1.[音频]

A. From a used car.
B. From Halfords.
C. From manufacturers.
D. From DIY store.

2

A. One weekend.
B. One week.
C. Ten days.
D. Half a month.

Questions 3 and 4 will be based on News ltem 2.[音频]

A. To track illegal dumps.
B. To track polluted areas.
C. To dectect wildfires.
D. To eat dumped rubbish.