The Primary Difference Between an American Call Option and a European

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

A) has a fixed strike price while the European strike price varies over time.
B) is a right to buy while a European call is an obligation to buy.
C) has an expiration date while the European call does not.
D) is written on 100 shares of the underlying security while the European call covers 10 shares.
E) can be exercised at any time prior to expiration while the European call can only be exercised on the expiration date.