設隨機變量X的分布律為P{X=k}=λλ]，k=0,1,2,...，則E[(X+1)(X+2)]= _______．

題目：設隨機變量X的分布律為P{X=k}=λλ]，k=0,1,2,...，則E[(X+1)(X+2)]= _______．
A. λ^2+3λ
B. λ^2+3λ+2
C. λ+3
D. λ^2+λ