If $x=y \cos \left(\frac{2 \pi}{3}\right)=z \cos \left(\frac{4 \pi}{3}\right)$, then what is $x y+y z+$ $z x$ equal to?

• A

  $-1$
• Correct answer
  B

  $0$
• C

  $1$
• D

  $2$

Hence, the correct answer is option: 'B'.