In 1999, Fredrick executed a will by which he devised his realty known as Texacre "to Aggie for life; and upon the death of Aggie as follows: a one-third interest to the children of Aggie, a one-third interest to the children of Bob, and a one-third interest to the children of Carl, but if any of Carl's children should fail to survive to the age of 25 years, then the interest of such child or children of Carl shall pass to all grandchildren of Carl equally, share and share alike."

At the time the will was signed, Aggie had a son named Timothy, Bob had two children named Molly and John, and Carl had no children.

When Fredrick died in 2012, what interest did Carl's children have in Texacre?

Select one:

a. Valid contingent remainder.

b. Contingent remainder.

c. Executory interest.

d. Vested remainder subject to divestment.