The answer is D. The program prints:
56

Why?
The loop remembers the biggest number it has seen so far, and replaces it whenever it finds a bigger one. This is how computers find the maximum.
Trace table
A trace table follows the program step by step. Here’s this one:
| n | n > biggest? | biggest |
|---|---|---|
| 19 | yes | 19 |
| 28 | yes | 28 |
| 56 | yes | 56 |
| 48 | no | 56 |
| 3 | no | 56 |
The code again
numbers = [19, 28, 56, 48, 3]
biggest = 0
for n in numbers:
if n > biggest:
biggest = n
print(biggest)
Try it: change one number in the program and predict the new output before you run it.