Three functions $f_{1}(t), f_{2}(t)$ and $f_{3}(t)$, which are zero outside the interval $[0, T]$, are shown in the figure. Which of the following statements is correct?
- $f_{1}(t)$ and $f_{2}(t)$ are orthogonal
- $f_{1}(t)$ and $f_{3}(t)$ are orthogonal
- $f_{2}(t)$ and $f_{3}(t)$ are orthogonal
- $f_{1}(t)$ and $f_{2}(t)$ are orthonormal