"We are eating, while you are drinking."

Translation: Nous mangeons, tandis que vous buvez.

[Cagrkr]

Why is not the third option right as well?

[laliga]

"que" is not followed by a vowel, so it should not contract to "qu'"
que+il=qu'il ("que" is followed by a vowel)
que+tu=que tu ("que" is not followed by a vowel)

[gnedge]

Tandis versus Pendant? I learned "pendant" when I was in school.. Has this since been superseded by tandis? are they interchangeable? if not, when would I use tandis que instead of pendant que?