The correct answer is: Both (A) and (B).
An open circuited armature coil of a D.C. machine is identified by the scarring of the commutator segment to which open circuited coil is connected. This is because the current flowing through the coil will cause the commutator segment to heat up and eventually wear away. The scarring can be seen as a dark spot on the commutator segment.
An open circuited armature coil of a D.C. machine is also indicated by a spark completely around the commutator. This is because the current flowing through the coil will cause the commutator segments to arc together. The spark can be seen as a bright flash of light.
Both of these symptoms can be used to identify an open circuited armature coil of a D.C. machine.