Choice Bhoice C is the correct answer.

1. Define variables: Let $x$ be the smallest. The others are $x+1$ and $x+2$.
2. Equation: $x + (x + 1) + (x + 2) = 36$
3. Combine: $3x + 3 = 36$
4. Subtract 3: $3x = 33$
5. Divide by 3: $x = 11$
6. Verify: $11 + 12 + 13 = 36$ ✓

Choice Bhoice D is incorrect because this is the middle integer.

Choice Bhoice D is incorrect because this is the largest integer.

Choice Bhoice A is incorrect because calculation error.