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Verbal·Standard English Conventions·Boundaries
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Seawater contains many trace elements that can be categorized in one of three ways based on their significance in sustaining living organisms: essential, possibly essential, or nonessential. Molybdenum, whose chemical symbol is        is classified as an essential element.
Which choice completes the text so that it conforms to the conventions of Standard English?
A
Mo
B
Mo:
C
Mo—
D
Mo,