4 During the Covid-19 pandemic, countries around the world immediately closed their borders, imposed export bans on vaccines and pharmaceutical equipment, and the U.S. and China competed on vaccine diplomacy. Which of the following best explains the phenomena above?
(A) Realism.
(B) Liberalism.
(C) Globalism.
(D) Protectionism.

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統計: A(13), B(0), C(1), D(2), E(0) #2771024