单项选择题
A.λD/dB.λd/DC.λD/(2d)D.λd/(2D)
A.2n2eB.2n2e-λ/2C.2n2e-λD.2n2e-λ/(2n2)
A.l=3λ/2,△φ=3πB.l=3λ/(2n),△φ=3nπC.l=3λ/(2n),△φ=3πD.l=3nλ/2,△φ=3nπ