Answer:
Sentence B shows a correct apostrophe use.
Step-by-step explanation:
The first apostrophe is the contraction of the verb to be in its singular form (is). Then, the second one, is the one indicating possession since it either denotes that Marta is the one throwing the party or the one to whom the party is thrown for. The general rule to form the possessive with an apostrophe is to add the apostrophe and -s. (Marta/Marta's).