Which of the following statements about zeolites is false ?

Options

A. They have open structure which enables them to take up small molecules.
B. Zeolites are aluminosilicates having three dimenstional network.
C. Some of the `SiO_4^(4-)` units are replaced by `AlO_4^(5-)` and `AlO_6^(9-)` ion in zeolites.
D. They are used as cation exchangers.