Final answer:
The question asks about the views of Anatoly Dyatlov, related to the Chernobyl disaster, but the provided text does not details Dyatlov's specific opinion on what mattered most. However, reactor temperature is an essential aspect of nuclear reactor safety.
Step-by-step explanation:
The question pertains to Anatoly Dyatlov, the deputy chief engineer at the Chernobyl Nuclear Power Plant during the disaster in 1986. The information provided emphasizes the critical aspects of nuclear reactor safety, such as the need for cooling, containment, and the impact of high temperatures and pressures. However, none of the provided texts specifically mention Dyatlov's opinion on the only thing that mattered. It's a historical inquiry related to a real-world event, and no option directly correlates with the provided references concerning Dyatlov's perspectives.
Nevertheless, in the broader context of nuclear safety, it can be inferred that reactor temperature is a critical factor that must be strictly controlled to prevent disasters. Cooling systems and other safety mechanisms like control rods and auxiliary pumps are essential for maintaining this temperature. Given the lack of information on Dyatlov's specific viewpoint, it would be inaccurate to attribute one of the options directly to him without further evidence.