Re: Two quick grammar questions
As a footnote:
1. I bought apples, bananas and oranges.
2. I bought apples, bananas, and oranges.
The second comma in #2 is called an "Oxford comma" or "serial comma". It was the standard punctuation in British English until the second half of the 20th century, and is still preferred by the Oxford University Press and some other publishers. (I believe it is also fairly standard in US publications.)
However, #1 is now more usual in BrE publications and ordinary business English, except in cases where confusion might arise, as J. suggests.
Not a professional ESL teacher.