French language Q&A Forum

This translation caught my attention as number doesn't agree:

Le duc et la duchesse accueilleront la Reine comme il se doit.The Duke and Duchess will greet the Queen as one should.

Why would this not be "comme on se doit" ? for "as one should"

Why is "horreur" singular in this instance, when the "films" aspect is plural? 

Does horreur ever need to change? E.g. if it was PL: films d'horreur vs SG: film d'horreur

Why is it "Vous avez faim, les enfants?" and not "Avez-vous faim, les enfants?"?

1. In the above sentence, why didn't we use the article partitive des?

A similar trend is seen in this sentence as well:

Une dernière idée est de recycler une râpe à fromage rouillée en (un?) présentoir à boucles d'oreille. 

2. making alterations ---> apporter des modifications? Is this a fixed expression in French?

If you drop the "s" from all "er" verbs when using the singular imperative, why does "ajoutes-y" have an "s" ?

Why is quite not plural inthe follwing sentence?

On va regarder des films d'horreur et faire des quiz sur le thème d'Halloween.

The literal meaning is something like "make pale with envy."  Is there a better translation?

Would you ever say "regarder à" to mean "look at"? Or is the "at" implied?

why "que ... d'autre" but not "que d'autre" like "qui d'autre, quoi d'autre"? Thanks.

There is really no explanation of how to distinguish when to use these properly.