Question

testing for concussions
when a patient is suspected of having a concussion, or brain injury, doctors often turn to computed tomography, or ct, scans to find out for sure. in a ct scan, a series of x - rays is taken. each one shows an individual “slice” of the brain, and they can be combined to form a complete three - dimensional picture. because of the amount of radiation patients are exposed to, however, doctors question the use of the scans, especially for children. now researchers have proposed an alternative way of diagnosing head injuries: a simple blood test. the test detects proteins that burst out of brain cells into the bloodstream immediately after an injury. it allows doctors to determine whether a patient has suffered head trauma and needs further treatment.
what is the main, or central, idea of the passage?
a new blood test makes it easier—and safer—to detect concussions.
a new blood test can identify proteins that are present in the blood following a brain injury.
doctors commonly use ct scans to test for brain injuries.

Explanation:

The passage first introduces that doctors use CT scans for concussion diagnosis but have concerns about radiation, then presents a new blood test as an alternative. The first option captures the main idea of the new blood test being a better (easier and safer) way to detect concussions. The second option is just a detail about the blood test, and the third is about CT scans which is a background detail, not the main idea.

Answer:

A. A new blood test makes it easier—and safer—to detect concussions.