The normal distribution is represented by N(μ, σ squared), and μ represents the central axis of the normal distribution (the symmetry axis of the graph). Refer to the figure below (note the position of μ, the graph is symmetrical about x=μ).

ξ obeys the normal distribution n (2,9), that is, the central axis (graphic symmetry axis) μ=2, and also obtains:

P(ξ>μ+ any number) = p(ξ c+ 1) = p (ξ < c- 1), then c=2, and choose B.