You have a two-dimensional list in the following format:
```python
data = [[2, 5], [3, 4], [8, 7]]
```
Each sub-list contains two items, and each item in the sub-lists is an integer.
Write a function `process_data()` that processes each sub-list like so:
 * `[2, 5]` --> `2 - 5` --> `-3`
 * `[3, 4]` --> `3 - 4` --> `-1`
 * `[8, 7]` --> `8 - 7` --> `1`
and then returns the product of all the processed sub-lists: `-3 * -1 * 1` --> `3`.
For input, you can trust that neither the main list nor the sublists will be empty.
def process_data(data):
    r = 1
    for d in data:
        r *= d[0] - d[1]
    return r
def process_data(data):
    r = 1
    for d in data:
        r *= d[0] - d[1]
    return r