Which expression represents the fourth term in the binomial expansion of (e + 2f)10?

In the binomial expansion of (e + 2f)^10, the term with index k is 10Ck · e^(10−k) · (2f)^k. The fourth term uses k = 3, so it is 10C3(e^7)(2f)^3, which is choice A.

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