24. Why does the passage give the example of Facebook and YouTube?
(A) To point out how global the world is rapidly becoming.
(B) To demonstrate the weaknesses in social-networking sites.
(C) To show how Facebook and YouTube create motivational ads.
(D) To provide examples of channels used to spread messages.

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統計： A(1), B(2), C(1), D(15), E(0) #1564001