Question

Punch your papers in a paper in a file, you may lose them. (Use: lest)

Answer 1

punch your papers in a file lest you may lose them 
is it right?

Answer 2

Answer :

This question is based on conjunctions.

Cambridge English Dictionary defines 'conjunction' as ' a word such as 'and', 'but', 'while', or 'although' that connects words, phrases, and clauses in a sentence.'

'Lest' is a conjunction, which according to the Cambridge English Dictionary, means 'in order to prevent any possibility that something will happen.'

So, the correct sentence, using the conjunction 'lest' is :

Punch your papers in a paper file lest you may lose them.