Consider the following Syntax Directed Translation Scheme (SDTS), with non-terminals $\{S, A\}$ and terminals $\{a, b\}$. $$\begin{aligned} S & \longrightarrow aA & \{\text{ print } 1 \} S & \longrightarrow a & \{\text{ print } 2 \} A & \longrightarrow Sb & \{\text{ print } 3 \} \end{aligned}$$ Using the above SDTS, the output printed by a bottom-up parser, for the input **aab** is:

In a bottom-up parser (such as shift-reduce parser), the semantic action associated with a production rule is executed when that production is reduced.

Given the input string aab:

1. Shift the first a onto the stack.

2. Shift the second a onto the stack.

3. Reduce the second a using $S \longrightarrow a$. The semantic action { print 2 } executes, printing 2. The stack now contains a S.

4. Shiftb onto the stack. The stack now contains a S b.

5. ReduceS b using $A \longrightarrow Sb$. The semantic action { print 3 } executes, printing 3. The stack now contains a A.

6. Reducea A using $S \longrightarrow aA$. The semantic action { print 1 } executes, printing 1. The stack now contains S (the start symbol).

Parsing completes successfully. Combining the printed outputs in order gives 2 3 1, which corresponds to option (C).