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. both a) and b)