When exchange rates change:
a. u. s. firms that produce domestically and sell only to domestic customers will be unaffected.
b. u. s. firms that produce domestically and sell only to domestic customers can be affected if they compete against imports.
c. u. s. firms that produce domestically and sell only to domestic customers will be affected, but only if they borrow in foreign currency to finance their domestic operations.
d. u. s. firms that produce domestically and sell only to domestic customers will be unaffected, and u. s. firms that produce domestically and sell only to domestic customers can be affected if they compete against imports.