For a plane electromagnetic wave,$E_x = 0$,$E_y = 2.5 \frac{N}{C} \cos \left[ (2\pi \times 10^6 \frac{rad}{s})t - (\pi \times 10^{-2} \frac{rad}{m})x \right]$,and $E_z = 0$. Which of the following is true?

• A
  The wave propagates in the positive $X$ direction with a wavelength of $100 \ m$ and a frequency of $10^6 \ Hz$.
• B
  The wave propagates in the positive $X$ direction with a wavelength of $200 \ m$ and a frequency of $10^6 \ Hz$.
• C
  The wave propagates in the negative $X$ direction with a wavelength of $200 \ m$ and a frequency of $10^6 \ Hz$.
• D
  The wave propagates in the positive $Y$ direction with a wavelength of $200 \ m$ and a frequency of $10^6 \ Hz$.