Belbin's management role

Belbn described the most effective character mix in a team. This involves eight necessary roles, which should ideally be balanced and spread in a team.
A person who is highly strung, extrovert and passionate about the task fits in
to which Belbin’s roles?
(i) Plant
(ii) Completer Finisher
(iii) Resource investigator
(iv) Shaper

A. (i), (ii) and (iii)
B. (ii), (iii) and (iv)
C. (i), (ii) and (iv)
D. (i), (iii) and (iv)

The correct is D. I know extrovert is the sign of Resource investigator and passionate is the sign of Shaper. But i don’t understand why strung is the sign of Plant.
Could you explain the assumption of the concept, Sir.

Thanks in advance.