How can you adjust the size of an array in C during runtime?

The ability to adjust the size of an array during runtime in C is achieved through dynamic memory allocation functions. This method allows programmers to request a specific amount of memory from the heap and manage the size of the array based on the program's requirements at any given moment.

When you use dynamic memory allocation functions such as malloc(), calloc(), realloc(), or free(), you can allocate memory of any size, change that amount, or deallocate it when it's no longer needed. For instance, malloc() allocates the specified amount of memory, while realloc() can change the size of an already allocated memory block, allowing for flexible resizing of the array.

In contrast, static arrays have a fixed size defined at compile-time and cannot be resized during the program's execution. They also consume stack memory, which limits the size you can allocate based on the stack's capacity. Global arrays are also static in nature; their size is determined at compile-time and cannot be adjusted. Therefore, the only method that allows for adjusting the size of an array at runtime is through dynamic memory allocation, making it the correct choice in this scenario.