Programming In C

Step 1: Understand the size of data types in C.
In C, the sizes of data types depend on the system architecture, but typically:

- **unsigned char** is the smallest data type, usually 1 byte.

- **unsigned int** typically takes 4 bytes on most systems.

- **signed long int** usually takes 4 bytes, but can take 8 bytes on some systems.

- **long double** is the largest, often taking 8 or 10 bytes depending on the system.

Step 2: Evaluate the options.
- **C (unsigned char)** is the smallest, so it comes first.

- **D (unsigned int)** is next in size, typically taking 4 bytes.

- **A (signed long int)** comes next, typically taking 4 or 8 bytes.

- **B (long double)** is the largest data type in C, typically taking 8 or 10 bytes.

Step 3: Conclusion.
Thus, the correct order from smallest to largest is: **C, D, A, B**.