The new serial interface card for the router arrives and the network technician reads that it is hotswappable. What does this mean?

The new serial interface card for the router arrives and the network technician reads that it is hotswappable. What does this mean?

• The card cannot be installed while the router is powered on because static discharge
  could damage the card.
• The card cannot be installed until the router is powered off and completely cooled down.
• The card can be installed while the router is powered on if the router supports this technology.
• The card is a replacement and must be installed in the same slot as the card it is
  replacing.

Exam with this question: CCNA Discovery 4: DCompNtwk Chapter 3 Exam