In this question, we will start a proof by induction to show that, for nonnegative integers n: 1 + 2 + 3+... +n+(n+1) = (n+1)(n+2) 2 Let P(n) be the proposition be the proposition above for nonnegative integers, n: 1. In the basis step, we need to show that [Select ] holds. 2. The basis step holds because [ Select ] 3. For the inductive step, we begin by [ Select ] for an arbitrary nonnegative integer, k. 4. So, in the inductive step, this means that we need to show which of the following below? [ Select ] 1. 1 + 2 + 3+. .. + (k+ 1) + (k+2) _ (k+2)(k+3) 2 11. 1 + 2 + 3+. . . + (k + 1) = (k+2)(k+3) 2 Ill. 1 = 1