Final answer:
The completed identity is sin(θ) (option B).
Step-by-step explanation:
The identity can be completed as follows:
cos(90° - θ) = cos(90°)cos(θ) + sin(90°)sin(θ)
Since cos(90°) = 0 and sin(90°) = 1, the expression simplifies to:
cos(90° - θ) = 0cos(θ) + 1sin(θ)
Therefore, the answer is sin(θ) (option B).