Concept:
Different categories of instructions exist in processors.
Step 1: Branch instructions
Used for changing program flow.
Step 2: Flag instructions
Used for manipulating status flags.
Step 3: Shift/rotate instructions
Used for bit-level operations.
Step 4: String instructions
Used for operations like move, compare, scan strings.
Step 5: Conclusion
\[
\boxed{\text{String instructions}}
\]
Final Answer:
\[
\boxed{(D)}
\]