Answer: c. 50%
Explanation:
If you draw a punnett square you see that the phenotypes you get are Cc, Cc, cc, and cc. If C (curly hair) is dominant over c (straight hair) then those with the phenotype Cc would have curly hair and those with the phenotype cc would have straight hair. 2 out of 4 have Cc (curly hair) so that's 50%.