Question

Complete the following sentence so that the subject agrees with the verb. _____ are going to sign up for tennis lessons. Gisela Gisela or Nina Gisela’s sister Gisela and Nina

Answer 1

Gisela and Nina

You have to have more than one subject because the linking verb

Answer 2

Gisela and Nina
You have to have more than one subject because the linking verb "are" is plural. You cannot have a singular noun and Gisela's is possessive (and singular) so it doesn't work.