Prepositions / Phrasal Verbs

[Emanuelli]

Hello!!!
I have three questions:
a) Can I use phrasal verbs in formal letters???

b) "On holidays my friends and I went riding". I saw in a book that this sentence is wrong. The correct form would be: "In the holidays, my friends and I went riding". Then I wonder to know why? I've looked the words "holiday" and "vacation" up in dictionaries but the only preposition I see is "on".

c) When I wish: "Have a nice vacation / holiday", I don't need to use it in the plural, do I?

Thanks.

[Tdol]

You can use phrasal verbs, but you shouldn't use too many in formal writing. If there is an easy replacement, then it's a good idea to replace.

On holiday
Without the definite article, we use 'on', bit with the definite article, we use 'in/during the holidays'
We use the plural for holidays for everybody:
I went on holiday to Spain.
What did you do during the Easter holidays?