We often use zero article with the names of holidays,special times of the year,or with the names of months and days of the week:

  -easter    -new year's day  -September  -Monday

but compare:

 -I'll see you on Saturday    

 - they arrived on  a Saturday as  far as I can  remember.     

 -they arrived on the Saturday after my birthday party.

With winter,summer,spring,autumn and new year (meaning the holiday period),we can often use either the or zero article:

 -in (the)summer I try to spend  much time in the garden.

 -in Scotland,they really know how to celebrate (the) new year.

We use the when it is understood which summer,spring,etc. we mean:   

 -'when did you meet Beth?' 'in the summer.' (=last summer)

 -'when are you going to university?' 'in the autumn.' (=next autumn)

 - I first went skiing in the spring of 1992.

We say 'in the new year' to mean at or near the beginning of next year:     

 - I'll see you again in the new year. 

When we want to describe the features of a particular holiday,season,etc.,

we use a/an:

 - that was a winter I'll never forget.

*Complete the sentences with a/an, the or zero article(0), whichever is most likely,in the spaces in

these sentences.