On an Aironet card， LED 0 and LED 1 are blinking alternately.  What does this indicate？ （）

• A、The Aironet card is in power save mode.
• B、The Aironet card is looking for a network association.
• C、The Aironet card is joined to a network， but there is no network activity.
• D、The Aironet card is joined to a network， and there is network activity.