Directions:

#include
# define a 10
void main()
{
    printf("%d..", a);
    foo();
    printf("%d", a);
}
void foo()
{
   #undef a
   #define a 50
}

Question:
What will be output after executing following code?

Option A):
Error
Option B):
0
Option C):
10..10
Option D):
10..50

Correct Answer is Option C):
10..10