Semantic Analyzer is a crucial phase in the compilation process, where the input is analyzed for its meaning and correctness. It performs various tasks such as type checking, scope resolution, and generating intermediate code. The semantic analyzer takes input in the form of a syntax tree and produces output in the form of a syntax tree.

The correct answer to the given question is option 'D' - Syntax tree, syntax tree.

Explanation:
- Syntax Tree: A syntax tree represents the syntactic structure of the input program. It is a hierarchical structure consisting of nodes that represent various elements of the program, such as expressions, statements, and declarations. The syntax tree is generated by the parser based on the grammar rules of the programming language.

- Semantic Analysis: Once the syntax tree is constructed, the semantic analyzer performs a deeper analysis of the program's structure to ensure its correctness and meaning. It checks for semantic errors, enforces type rules, resolves variable scopes, and generates intermediate representation for further processing.

- Input to Semantic Analyzer: The input to the semantic analyzer is the syntax tree generated by the parser. The syntax tree captures the structure and organization of the program, but it does not contain information about the program's meaning or correctness. Therefore, the semantic analyzer takes the syntax tree as input to perform semantic analysis.

- Output from Semantic Analyzer: The output produced by the semantic analyzer is an enhanced syntax tree that includes additional semantic information. This enhanced syntax tree represents not only the syntactic structure but also the meaning and correctness of the program. It contains type annotations, scope information, and other semantic details.

- Syntax Tree as Output: The output of the semantic analyzer is still represented in the form of a syntax tree. However, this syntax tree is different from the input syntax tree as it includes additional semantic information. It serves as an intermediate representation for further compilation stages such as code optimization and code generation.

Hence, the correct answer is option 'D' - Syntax tree, syntax tree.