What does the passage mainly discuss？
A. The scarcity of manufactured goods.
B. The value of martials.
C. The manufacturing of scarce goods.
D. The cost of producing shoes.
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Why does the author mention the Biograph Company？
A. To identify the most successful company in the film industry at the time.
B. To describe an exception to a trend in film exhibition in the early 1900s.
C. To discuss the first addition of films to traditional entertainment programs.
D. To illustrate the model on which most other small film companies were based.
Listen again to part of the lecture．Then answer the question. What does the professor imply about the behavior. of the snakes？
A. The snakes' behavior. is a warning signal to other animals.
B. Temperature plays an important role in the snakes' behavior.
C. Scientists can observe the snakes' behavior. in their winter dens.
D. The snakes are able to learn a variety of behavioral responses.
The word them in the passage refers to
A. less-developed nations.
B. individuals.
C. bonds.
D. primary groups.
Why does the professor say this:
A. To praise the area's beautiful winter scenery
B. To persuade students to build their own homes
C. To describe the most common one of limestone
D. To explain why so many snakes live in the region
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