Final answer:
Nereus was a hybrid underwater vehicle with both remotely operated and autonomous capabilities, making the statement that it is merely an ROV false.
Step-by-step explanation:
The statement that Nereus is simply an unmanned deep-sea remotely operated vehicle (ROV) is false. Nereus was actually a hybrid underwater vehicle that could operate both as an ROV and as an autonomous underwater vehicle (AUV). This dual capability allowed Nereus to be controlled remotely by operators via a tether for detailed tasks, or to operate independently according to pre-programmed instructions during deep-sea explorations.