Let's solve the problem step-by-step:

1. Set Up the Problem:
- Let the two numbers be \(3x\) and \(5x\) respectively, where they are in the ratio 3:5.
- According to the problem, if 9 is subtracted from each number, their ratio becomes 12:23.

2. Form the Equation:
- After subtracting 9 from each number, the new ratio is given by:
\[
\frac{3x - 9}{5x - 9} = \frac{12}{23}
\]

3. Cross-Multiply to Solve:
- Cross-multiplying gives:
\[
23(3x - 9) = 12(5x - 9)
\]
- Expanding both sides:
\[
69x - 207 = 60x - 108
\]
- Solving for \(x\):
\[
69x - 60x = 207 - 108
\]
\[
9x = 99
\]
\[
x = 11
\]

4. Find the Numbers:
- The smaller number is \(3x\):
\[
3x = 3 \times 11 = 33
\]


The smaller number is 33.

The correct answer is B. 33.