A: Root Cause Analysis: Looking at the given vulnerable code line and its context, the CWE-401 (Missing Release of Memory after Effective Lifetime) vulnerability exists in the code because the `destination` buffer is allocated memory using `calloc` at line 6, but there is no corresponding `free` call to release the memory allocated for `destination` before the function returns. This can lead to memory leaks as the allocated memory is not released after its effective lifetime.