Which of the following statements in Not true
A．The new commercial bike has no crossbar and its centre of gravity is lower than the Olympic model.
B．When the rider is doing some rough riding, the new bike's low cetnre of gravity gives him better control.
C．The new bike is made by using aerospace technology and is quicker than the conventional bike by 3 seconds per kilometer.
D．The new bike has no metal bar between the saddle and the back wheel, and the amount of carbon fibre in the back wheel can be changed according to the user's tast