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Spongebob can roll his tongue. His evil twin brother cannot. Which statement explains why?
a. Spongebob can do it because he is older?
b. Spongebob has a dominant factor for tongue-rolling
c. The evil twin can't because he hasn't practiced enough yet
d. The evil twin has a dominant and a recessive factor for tongue-rolling
b. Spongebob has a dominant factor for tongue-rolling