<ref>Daniels, J., Radebaugh, L., Sullivan, D. (2007). International Business: environment and operations, 11th edition. Prentice Hall. ISBN 0-13-186942-6</ref> | <ref>Daniels, J., Radebaugh, L., Sullivan, D. (2007). International Business: environment and operations, 11th edition. Prentice Hall. ISBN 0-13-186942-6</ref> |