What is the value of the variable phones after the following code executes?
```python
phones = 'john' : '5555555', 'julie' : '5557777'
phones['john'] = 5556666
```
a) 'john': '5555555', 'julie': '5557777'
b) 'john': 5556666, 'julie': '5557777'
c) 'john': '5556666', 'julie': '5557777'
d) 'john': '5555555', 'julie': 5556666