In S.I. engine if the spark plug deposit indicates black coating of soot, it therefore indicates that the engine has been generally operating on

In S.I. engine if the spark plug deposit indicates black coating of so

1.	In S.I. engine if the spark plug deposit indicates black coating of soot, it therefore indicates that the engine has been generally operating on
A.	Too rich mixture
B.	Most economical mixture
C.	Too lean mixture
D.	Slightly rich mixture
E.	Stoichiometric mixture
Answer» B. Most economical mixture