Answer:
The answer D (i'm french trust me)
Step-by-step explanation:
The answer A could have been true but in this case that means 2 pronouns (it's possible but you'll see that later) so it's not this one.
The answer B is wrong because "il" = he and "elle" = she, Sophie is a woman so it can't be this one (plus it's the same case that there was in the answer A)
The answer C is wrong too, because it's in plural and there's only one Sophie.
The answer D is true, because were using the singular and not another pronouns. ("ce" and "c'" are called demonstratives pronouns, they're used too show, demonstrate something or someone.
Exemple : "What's on the table ?" will be :
"C'est quoi sur la table ?"
Or "Who wrote this book ?" :
"Qui est-ce qui à écrit ce livre ?")