Answer: C
\[ (\sin\theta + \cos\theta)^2 \\ = \sin^2\theta + \cos^2\theta + 2\sin\theta \cos\theta \\ = 1 + 2 \times \frac{1}{2} \\ = 1 + 1 \\ = 2 \]
\[ (\sin\theta + \cos\theta)^2 \\ = \sin^2\theta + \cos^2\theta + 2\sin\theta \cos\theta \\ = 1 + 2 \times \frac{1}{2} \\ = 1 + 1 \\ = 2 \]