Pivot mean the central point, pin, or shaft on which a mechanism turns or oscillates.
The antecedent of a pronoun is basically the noun that a pronoun replaces, AKA the noun that the pronoun refers to. It should be somewhere before the pronoun in the sentence. In the sentence "Strikers will return to work when the union representative has completed their name negotiation," the pronoun is "their." Whose name negotiation is being completed? The strikers. This could read, "Strikers will return to work when the union representative has completed THE STRIKERS' name negotiation." That works! So, the pronoun "their" refers to the strikers.
Answer: strikers
