For a transverse wave on a string the string displacement is described by $\backslash ($ y$($x$,$ t$)=$f$($x$-$a t$)\backslash ),$ where $\backslash ($ f $\backslash )$ is a given function and $\backslash ($ a $\backslash )$ is a positive constant. Which of the following does NOT necessarily follow from this statement? A$.$ The shape of the string at time $\backslash ($ t$=0\backslash )$ is given by $\backslash ($ f$($x$)\backslash ).$ B$.$ The shape of the waveform does not change as it moves along the string. C$.$ The waveform moves in the positive $\backslash ($ x $\backslash )$ direction. D$.$ The speed of the waveform is $\backslash ($ a $\backslash ).$ E$.$ The speed of the waveform is $\backslash ($ x $/$ t $\backslash ).$