"était" versus "c'était"

Question

In writing challenge week 68 B2, one of the correct answers is "Oui, je crois que la dernière fois, c’était chez Paul et Sophie." as opposed to "Oui, je crois que la dernière fois était chez Paul et Sophie." What are the rules for using c'est and its variations when in the middle of a sentence?

Answer

Bonjour Michelle,
Je pense que la réponse est dans la leçon:
1. c'est  in sentences it/he/she is + a/the/my... + thing/people If it/he/she is is followed by un/une/le/la... (any form of article / determinant) - it is a beautiful dress / she is a nice person - then you will use c'est.
2. Cases expressing opinions or simple statements (adjectives) about prementioned things, look at these rules:
a - c'est  for general, unspecific statements and opinions
In those cases, we're expressing opinions or statements that refer to the thing generally: we're saying science in general is thrilling, or that something unspecified is great or delicious. 
Therefore, here we use c'est to say it is.
b - il est/elle est  for statements and opinions related to specific things In those cases, the opinions expressed relate to specific items, we know precisely what we're talking about, whether it be my jumper (not jumpers in general), your plate or that specific bed.
Therefore, here we use il est or elle est, depending on the gender of the thing it refers to (remember that things have genders too in French!).
And here is an example with «c'est» in the middle of a sentence:
Miam, c'est délicieux!
Yummy, it's delicious!
J'espère que cela vous aiderait.
Bonne chance,