Ask what has to happen when a segment goes missing. Detecting loss is not enough; the data must be resent. TCP achieves this with a feedback system.
Every byte carries a sequence number, and the receiver replies with an acknowledgment number confirming what arrived. The sender starts a retransmission timer; if no ACK returns in time, it resends:
\[ \text{No ACK before timeout} \Rightarrow \text{retransmit segment} \]
Checksums only flag corruption and best-effort delivery gives no recovery at all, so neither guarantees reliability by itself. Packet flooding is unrelated.
\[\boxed{\text{Acknowledgments and retransmissions}}\]