Language/French/Grammar/"C'est"-or-"Ce-sont"

When use "C'est", When use "Ce sont" ?

Impersonal expressions

These expressions, constructed with the pronoun "ce" (or its abbreviated "c'") and the verb "être", are said to be impersonal.

The pronoun 'ce' is the apparent subject of the verb to be, but the real subject is a word or a group of words after the verb.

Example:

• Ce sont eux qui les ont conduits. Oui, c'est bien nous qui les avons conduits.

They are the ones who led them. Yes, it is we who led them.

"être" agrees with 'ce'

Generally, the verb "être" agrees with the apparent subject 'ce'.

Example:

• Ce n'est pas moi, mais c'est lui qui a mangé tout le chocolat. C'est vous qui avez commencé. Est-ce toi qui as crié ?

It was not me, but he was the one who ate all the chocolate. You started it. Did you scream?

Agreement with the real subject in the third person plural

However, in the case where the real subject (actually doing the action) is a noun or noun in the third person plural, then the verb "être" agrees with its real subject in the third person plural, except in some cases (see below).

Example:

• Ce sont tes parents au téléphone.

It's your parents on the phone.

Spoken language: "c'est" instead of "ce sont"

In spoken language, it can sometimes be accepted to match the verb with the apparent subject 'ce' when the real subject is 'eux' or 'ceux' or an enumeration yet in the third person plural.

Examples:

• Ce sont toujours eux qui font du bruit. Dans la langue parlée, il peut parfois être admis de dire : C'est toujours eux qui font du bruit.

They are always the ones who make the noise. In the spoken language, it can sometimes be accepted to say: It is always they who make the noise.

• Quels sont vos loisirs préférés ? Pour moi, ce sont le tennis et la natation.

What are your favourite hobbies ? For me it is tennis and swimming.

In the spoken language it may sometimes be accepted to say:

• Pour moi, c'est le dessin et la musique.

Frozen expressions

Some expressions tend to stay in the present tense more and more often. Example:

• "qui paiera la facture ? C'est moi !" NOT "ce sera moi !"

who will pay the bill? It's me!

Finally, some expressions are frozen by use:

• si ce n'est,

if not

• si ce n'était

if it were not

• n'est-ce pas?

is it not?

• est-ce que

is it

• serait-ce

would it be

• fût-ce

was it

• c'est-à-dire

that's to say

c'est	ce sont	ce sont (c'est)	frozen expressions
in general	real subject in 3rd person plural	preferably "ce sont" but the spoken language sometimes admits 'c'est' when the actual subject is 'eux', 'ceux' or an enumeration	si ce n'est, si ce n'était, n'est-ce pas, est-ce que, serait-ce, fût-ce, c'est-à-dire, etc.

Source

https://www.francaisfacile.com/exercices/exercice-francais-2/exercice-francais-3555.php