The fundamental difference between symmetric and asymmetric key cryptographic systems is that symmetric key cryptography uses which of the following?

Using multiple keys for non-repudiation describes a property of asymmetric cryptography, not symmetric, since non-repudiation relies on a private key that only one party holds.

Using different keys on each end of the transmission describes asymmetric cryptography, where a public key encrypts and a different private key decrypts.

Bulk encryption capability is a performance characteristic of some symmetric ciphers, but it is not the defining difference between symmetric and asymmetric systems, and fiber medium is irrelevant.

Symmetric cryptography relies on a single shared secret key that both the sender and receiver must possess. This shared key is used for both encryption and decryption, which is the defining characteristic separating it from asymmetric (public-key) systems. The requirement for both parties to hold the same key creates the well-known key distribution problem.