If the cell body of a pns neuron survives when an axon is damaged, axon filaments can extend peripherally from the injured site toward the original target.

The statement above is TRUE.
The peripheral extension of an axon filament from an injured site toward an original target is an example of axonal regeneration. Axon regeneration in the matured mammalian central nervous system is very limited after injury. But axonal regeneration is still possible in some instances such as the one given in this question.

answer: - b cells

explanation: -

there are many types of white blood cells present in our body. one such class of white blood cells are the lymphocytes. the b cells belong to the lymphocyte class of wbcs. the b cells perform their action against the pathogen by producing specialised proteins called as antibodies. these antibodies are produced as and when the b cells encounter pathogens in response to the antigens present on the surface of the pathogen. these antibodies bind to the antigens present on the pathogen and then, target them for destruction by other cells of the immune system.

so, the b cells mediate their action by identifying the antigens present on the surface of the pathogens and then producing antibodies in return to mediate its effect.