Which of the following statements is true?

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a. Developing countries rely more heavily on direct taxes than do developed countries.

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b. Developing countries rely more heavily on indirect taxes than do developed countries.

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c. Developing countries rely more heavily on personal income taxes than do developed countries.

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d. Developing countries rely more heavily on social security taxes than do developed countries.

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e. Developed countries rely more heavily on import and export taxes than do developing countries.