What is an important concept when creating a reliable data transfer protocol?

Question $5$ options:

The layer$($s$)$ below the reliable data transfer protocol may be unreliable.

Reliable data transfer protocols don't adapt to changing network conditions.

Reliable data transfer protocols should focus solely on getting the data across as quickly as possible.

In a reliable data transfer protocol, packet order is not important and does not affect the integrity of the data received.

Reliable data transfer protocols do not need to manage congestion control, as it is solely the responsibility of network routers.