Read the following passage and mark the letter A, B, C, or D to indicate the answer to each of the question.

The hours we spend scrolling through our smartphones appear to be changing the shape of our skulls. This may be the reason why some people — especially the younger crowd — are developing a weird, bony spike just above their necks. This spike, known as an external occipital protuberance, appears at the lower end of the skull, and is sometimes so large, you can feel it by pressing your fingers on the base of your skull.

A study published in the Journal of Anatomy found that the spike was becoming more frequent — especially among 18 to 30-year-olds. David Shahar, the Australian health scientists who conducted the research, believes the development was triggered by prolonged use of smartphones or tablets. As people tilt their head forward to look at the screen, they put pressure on where the neck muscles meet the skull, so the body then develops more bone layers to be able to withstand it, said Shahar.

In the study, Shahar and a colleague looked at the radiographs of 218 young patients, aged 18 to 30, to determine how many had these spikes. In all, 41% of the group had an enlarged spike and 10% had an especially large spike measuring at least 0.7 inches (20 mm), the doctors found. In general, enlarged spikes were more common in males than in females. The largest spike belonged to a man, sticking out at 1.4 inches (35.7 mm).

Shahar believes that the spikes will continue to grow in size as people keep hunching over their handheld devices, but adds that they should not be very harmful and rarely cause serious medical issues. “But if you are experiencing discomfort, maybe you should try improving your posture,” he said.

(Adapted from breakingnewsenglish.com)

The word “it” in paragraph 2 refers to _______.