6. Read this sentence from the text.
"Though Plymouth would never develop as robust an economy as later settlements-such
as Massachusetts Bay Colony-agriculture, fishing and trading made the colony self-
sufficient within five years after it was founded."
Why might the author have used em dashes in this sentence?
A. to provide an example of one of the "later settlements"
B. to suggest that later settlements would take more than five years to become self-sufficient
C. to express surprise that Plymouth Colony's economy was not more robust
D. to emphasize the importance of agriculture in Plymouth Colony