Consider the following function written in the C programming language.void foo(char *a){ if ( *a && *a != ' '){ foo(a+1); putchar(*a); } }The output of the above function on input "ABCD EFGH" is

The function foo(char *a) recursively traverses characters until it reaches either the null terminator \0 or a space character ' ':

1. foo("ABCD EFGH") sees *a = 'A', calls foo("BCD EFGH").

2. foo("BCD EFGH") sees *a = 'B', calls foo("CD EFGH").

3. foo("CD EFGH") sees *a = 'C', calls foo("D EFGH").

4. foo("D EFGH") sees *a = 'D', calls foo(" EFGH").

5. foo(" EFGH") sees *a = ' ' (space), so the condition *a != ' ' is false and the function returns without printing.

As the recursion unwinds, putchar(*a) prints each character in reverse order:

• putchar('D') $\to$ prints D

• putchar('C') $\to$ prints C

• putchar('B') $\to$ prints B

• putchar('A') $\to$ prints A

Thus, the printed output is DCBA, which corresponds to Option (D).