Which sentence uses a verb that agrees with its subject?

the post offices in our area opens at 9 a. m.

their behavior during the performances was very good.

a new book by ruth randell, the author of many mysteries, arrive in bookstores soon.

the dresses on the rack in the back of the department was on sale.

Read the passage. when mother’s fever persisted for a week, father summoned our family doctor. dr. blakemore applied leeches to mother’s skin in hopes of reducing the amount of blood in her body. despite the doctor’s efforts, she languished in bed for three more days before her appetite returned and she requested a thin broth. our dear cook, mrs. davis, prepared the broth and delivered it to my mother directly, eager to ease her discomfort. what can readers infer about the time period of the passage?