Which of the Following Is the Best Definition of American

Which of the following is the best definition of American options.

A) A call or put option that can be exercised on or before its expiration date.
B) The condition stating that the expected percentage change in the exchange rate is equal to the difference in interest rates.
C) The condition stating that the current forward rate is an unbiased predictor of the future exchange rate.
D) Agreements to exchange two securities or currencies.
E) An agreement to trade currencies based on the exchange rate today for settlement in two days.