- A$\frac{1}{2}\big[\text{f(2}\text{x})+\text{f}(2\text{y})\big]$
- B$\frac{1}{2}\big[\text{f(2}\text{x})-\text{f}(2\text{y})\big]$
- C$\frac{1}{4}\big[\text{f(2}\text{x})+\text{f}(2\text{y})\big]$
- D$\frac{1}{4}\big[\text{f(2}\text{x})-\text{f}(2\text{y})\big]$