$A$ wave travelling along a uniform string represented by $Y=A \sin (\omega t-k x)$ is superimposed on another wave travelling along the same string represented by $Y=A \sin (\omega t+k x)$. The resultant is

• A
  $A$ wave travelling along $+x$ direction.
• B
  $A$ standing wave having nodes at $x=\left(n+\frac{1}{2}\right) \frac{\lambda}{2}$,where $n=0, 1, 2, 3, \ldots$
• C
  $A$ wave travelling along $-x$ direction.
• D
  $A$ standing wave having nodes at $x=\frac{n \lambda}{2}$,where $n=0, 1, 2, 3, \ldots$