If the spark plug deposit indicates black coating of soot, it indicates that the engine has been generally operating on

Question: If the spark plug deposit indicates black coating of soot, it indicates that the engine has been generally operating on
[A].

too lean mixture

[B].

stoichiometric mixture

[C].

most economical mixture

[D].

too rich mixture

Answer: Option D

Explanation:

No answer description available for this question.