Question
20 to 20 are based on this passage
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Question 20
According to the passage, when does the author believe the Oxford comma should be used?
A. It should always be used.
B. It should never be used.
C. It should be used only in some formats of writing.
D. It should be used to avoid ambiguity.
E. It is up to the writer's preference.
我的答案： 无