Oops, try again. flatten([[1, 2], [3, 4]]) returned [1] instead of [1, 2, 3, 4]

It prints

[1]

None

I tried replacing **number** with **numbers** in results.append(**number**)

Can't see any other errors..

```
n = [[1, 2, 3], [4, 5, 6, 7, 8, 9]]
# Add your function here
def flatten(lists):
results = []
for numbers in lists:
for number in numbers:
results.append(number)
return results
print flatten(n)
```