The inductive step of an inductive proof shows that for k ≥ 4 , if k! ≥ 2
k
, then (k +

1)! ≥ 2
k+1
.

However the lines are not labeled with the proper justification.
Which line should be labeled "Because k ≥ 4 ≥ 1 "?

(k + 1)! ≥ (k + 1) ⋅ k ⋅ (k − 1) ⋯ 2 ⋅ 1 (Step 1)
(k + 1)! ≥ (k + 1) ⋅ k! (Step 2)
(k + 1)! ≥ (k + 1) ⋅ 2
k

(Step 3)

(k + 1)! ≥ 2 ⋅ 2
k

(Step 4)

(k + 1)! ≥ 2
k+1

(Step 5)

a. Step 2
b. Step 3
c. Step 4
d. Step 5