Sickle-cell disease is a disorder that is caused by
A. a single mutation on a single gene.
B. a collection of mutations that span several different genes.
C. a collection of genetic mutations and environmental factors.
D. a collection of mutations on a single gene.
Answer: A
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A:________B:________C:________D:________E:________F:________G:________H:________I:________J:________K:________L:________M:________
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