A、Cotton. B、Coffee. C、Iron. D、Rubber. C注意提问中的否定副词not。而四个选项中只有Iron未提及，故应选择选项C。

Cameroon in West Africa is a nation of 24 separate languages and 200 tribal groups. The nation is also divided by three religions which compete for the loyalty of the 8 million people. However, Cameroon has managed to avoid problems with these ethnic and religious groups. This is partly due to its powerful president who has led the nation with authority for many years. In the past 10 years, Cameroon has also developed  a strong economy. Rubber, coffee, bananas, and cotton  are among the major products that give economic security to the country.