Akari is four years older than twice her sister Keira's age. The sum of their ages is 10. If Keira's age is represented by k, which expression represents the sum of their ages?
(A) k+ (6k) = 10
(B) 2k + 4 = 10
(C) k+(2k + 4) = 10
(D) k (2k + 4) = 10