Final answer:
The suitable engine lubricant for use in an engine equipped with a DPF is the one that meets the API CJ-4 specification.
Step-by-step explanation:
The suitable engine lubricant for use in an engine equipped with a DPF (Diesel Particulate Filter) is the one that meets the API CJ-4 specification. Therefore, option d. API CJ-4 is the correct choice.
Learn more about Engine lubricants for engines with DPF