The fourth term of the binomial expansion [tex](e+2f)^{10}[/tex] can be calculated using the formula for (i+1)-th term of the binomial expansion:
[tex]T_{i+1}=C_{10}^i\cdot e^{10-i}\cdot (2f)^i.[/tex]
In order to find term [tex]T_4[/tex], determine that
[tex]i+1=4\Rightarrow i=3.[/tex]
Now
[tex]T_4=C_{10}^3\cdot e^{10-3}\cdot (2f)^3=C_{10}^3\cdot e^7\cdot (2f)^3.[/tex]
Answer: correct choice is A
