What role does voir dire—french for to speak the truth—play in a trial?

to guide the jury when there is a question of law during deliberations
to allow attorneys to question witnesses to find out what they know about the case.
to the attorneys for both sides choose jurors appropriate for the case.
to enable the judge to object when a witness is lying on the stand.

To help the attorneys for both sides chooses Jurors appropriate for the case.

Explanation:

Prospective Jurors are examined by the attorneys with a series of questions to determine whether they are appropriate to judge a case without expressing any impartiality or bias. Voir dire is the inquisitorial method which is conducted by the legal solicitors based on which they may select a juror or reject them.  

Voir Dire analyses are critical and significant which is equal to the presentation of evidence in a case. A trial judge along with the attorneys can pose questions to the potential jurors to evaluate whether they are fair and open minded or have possessed preconceived notions about a particular case.

you are very ugly bro

explanation:

because the vietnam war was fought in an especially brutal and untraditional way