$\tan \frac{2 \pi}{7} \cdot \tan \frac{4 \pi}{7}+\tan \frac{4 \pi}{7} \cdot \tan \frac{\pi}{7}+\tan \frac{\pi}{7} \cdot \tan \frac{2 \pi}{7}=$

• A

  $7$
• Correct answer
  B

  $-7$
• C

  $3$
• D

  $-3$

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