To my mind , the best grammatical correction is " on " or " while " both of which are right "

Just ask me why ? follow me
DURING

• During is followed by a noun.
  It means 'throughout the period' or 'in the course of' an action or event.
  
  
  • During the summer I go to the beach as often as possible.
  • Exercises were given to us during the lesson.
  • The bank was robbed during the night.

WHILE

• While is followed by a subect and a verb.
  It means 'during the time that an action was taking place'.
  
  • They held hands while they were watching the film..
  • The students took notes while the teacher was speaking.
  • We'll collect some seashells while we're walking on the beach.
  • It is followed by " gerund " when there's no subject
    
  • some illustrating examples
    

Instructions: Clue-
'During' is a preposition
and 'while' is a conjunction.


Q1 - We met ___ the Xmas holidays.
http://static.usingenglish.com/images/tickbox.gif during
http://static.usingenglish.com/images/tickbox.gif while


Q2 - I learned French ____ I was working in a wine bar in Paris.
http://static.usingenglish.com/images/tickbox.gif during
http://static.usingenglish.com/images/tickbox.gif while


Q3 - It happened ____ I was out.
http://static.usingenglish.com/images/tickbox.gif during
http://static.usingenglish.com/images/tickbox.gif while


Q4 - It happened ____ my lunchbreak.
http://static.usingenglish.com/images/tickbox.gif during
http://static.usingenglish.com/images/tickbox.gif while


Q5 - It happened ___ the flooding.
http://static.usingenglish.com/images/tickbox.gif during
http://static.usingenglish.com/images/tickbox.gif while


Q6 - It happened ___ the floods.
http://static.usingenglish.com/images/tickbox.gif during
http://static.usingenglish.com/images/tickbox.gif while


Q7 - I fell alseep _____ the film.
http://static.usingenglish.com/images/tickbox.gif during
http://static.usingenglish.com/images/tickbox.gif while


Q8 - I fell alseep _____ I was watching the film.
http://static.usingenglish.com/images/tickbox.gif during
http://static.usingenglish.com/images/tickbox.gif while


Q9 - We had a lot of trouble ____ the journey.
http://static.usingenglish.com/images/tickbox.gif during
http://static.usingenglish.com/images/tickbox.gif while


Q10 - ____ working there, I met some really nice people.
http://static.usingenglish.com/images/tickbox.gif During
http://static.usingenglish.com/images/tickbox.gif While