What is a possible key size for the symmetric stream cipher RC4?

The correct answer identifies the key size range for the symmetric stream cipher RC4. RC4 supports key sizes that can go up to 2048 bits, which makes option B the most accurate in reflecting the capabilities of this cipher.

In practice, while some implementations may favor key sizes of 40 bits to 128 bits, the theoretical range established by the design of RC4 does indeed extend to 2048 bits. This flexibility allows developers to choose a key length that balances security with performance needs.

The other options, while they show key lengths that are technically valid in various contexts, do not encompass the full potential range of RC4's capabilities. Therefore, the key size range of 8-2048 bits accurately represents the choices available for this stream cipher.