Which data structure is used to store information about the source program constructs?

The question asks which data structure is used to store information about source program constructs. This refers to how compilers and interpreters represent the structure of code.

• A. 2d-array: A 2D array is a grid-like structure, suitable for tabular data, but not for representing the hierarchical relationships within program code.
• B. Stack: A stack is a Last-In, First-Out (LIFO) data structure. While stacks are crucial in compilers for tasks like managing function calls, evaluating expressions, and parsing, they do not store the overall structural information of the entire source program constructs.
• C. Tree: A tree data structure is hierarchical, with a root node and branches. This structure is perfectly suited to represent the nested and hierarchical nature of source code. Compilers commonly use an Abstract Syntax Tree (AST), which is a tree representation of the abstract syntactic structure of source code. Each node in the AST represents a construct in the source code (e.g., an expression, a statement, a declaration).
• D. Queue: A queue is a First-In, First-Out (FIFO) data structure. Queues are used in some compiler phases, but not as the primary structure for representing the entire program's constructs.

Therefore, a tree is the most appropriate data structure for storing information about source program constructs due to its ability to represent hierarchical relationships.

The final answer is $\boxed{\text{C}}$