Final answer:
To create a new file, use the open function with 'w' for write mode, and to add to an existing file, use 'a' for append mode. The letter 'W' is incorrect as the modes are case sensitive, and 'a' enables appending to a file.
Step-by-step explanation:
To create a new file in Python, you can use the built-in open function with the appropriate mode. There are multiple modes available for opening a file. The correct syntax for opening a file in write mode, which creates a new file if it does not exist or truncates the file if it does exist, is:
aFile = open("stuff.txt", "w")
Therefore, the correct letter to fill in the code is 'w', not 'W', as file mode arguments are case sensitive in Python. For the second question, when you wish to add to an existing file, you should use the append mode. The correct line of code should be:
myFile = open("another.txt", "a")
The letter 'a' in the open function stands for append mode, which allows you to add new content to the end of an existing file without overwriting its current contents.