下列说法不正确的是：

A．生物的遗传和变异是普遍存在的

B．镰刀型贫血病患者的遗传物质发生了变化

C．非近亲结婚所生子女肯定不会患遗传病

D．遗传病是一种可遗传的变异

Asynchronous Transfer Mode (ATM) is a (16) that promises to change the fabric of local and wide area communications.

The key advantage of ATM is the capability to move voice, data, graphics and (17) at speeds of up to 2 gigabits per second.

An ATM switch allows you to create a (18) network that is completely independent from the (19) configuration of the network.ATM uses a (20) called cell switching to convert data into fixed length cells of 53 bytes each, so they can be switched very quickly and efficiently.

（17）是（）

A. technology

B. video images

C. logical

D. physical