The Difference Between an American Option and a European Option

The difference between an American option and a European option is that the American option:

A) has a fixed exercise price while the European exercise price can vary within a small range.
B) is a right to buy while a European option is an obligation to buy.
C) has an expiration date while the European option does not.
D) is written on 100 shares of the underlying security while the European option covers 1,000 shares.
E) can be exercised at any time up to the expiration date while the European option can only be exercised on the expiration date.