A 28-year-old female presents to the ED with a complaint of left lower abdominal pain and vaginal bleeding. She has a history of irregular menses. She has 2 healthy children at home. Which of the following tests would narrow the differential and help determine disposition?
(A) Complete blood count.
(B) $\beta$-HCG .
(C) Urinalysis.
(D) $\mathrm{Rh}$ factor.