History of heartburn, now hypotension (507/1700)

A 45yo man had cancer of head of pancreas which has been removed. He has a hx of
longstanding heartburn. He now comes with rigid abdomen which is tender, temp 37.5C,
BP=90/70mmHg, pulse=120bpm. What is the next step of the inv?
a. CT abdomen
b. XR abdomen
c. MRI abdomen
d. US abdomen
e. Endoscopy

answer: B

Suspected perforated ulcer, X-ray will show free air under the diaphragm