For American options on futures:
Note that a forward contract does not pay off until expiration, in contrast to the mark-to-market procedure of futures contracts. Therefore, it's not worthwhile to exercise an American call or put on a forward contract as doing so would only establish a long or short position in a forward contract and would not pay any cash until expiration.
A. a higher price than, a higher price than.
If it's worthwhile to exercise an American option earlier, it should carry a higher price than its European counterpart.
A. make early exercise less likely.
Cash flows from the underlying are the only reason for early exercise of a call.
I. Dividends if the underlying is a stock.
A. Cash payments on the underlying.
Cash payments on the underlying are the only reason to exercise American calls early.
Carrying costs discourage exercise for American calls and encourage exercise for American puts.