O conveys Blackacre "to A for life, then to B and his heirs unless B dies before reaching age 21, and if B does die before reaching 21 to C and his heirs." When A dies, B is 15 years old.
Applying the Doctrine of Destructibility of Contingent Remainders, which statement is correct?

a. B’s interest failed within 21 years of A’s death, so B’s interest is valid.
b. B’s interest is destroyed because he did not reach 21 before A died, but C’s interest vested because it was an alternative contingent remainder.
c. B’s interest is not destroyed until his interest actually vests or fails by reaching or not reaching 21.
d. Both B’s interest and C’s interests are destroyed. O takes the property in fee simple absolute.
e. Both B’s interest and C’s interest are destroyed and A’s heirs will take the property in fee simple absolute.