Choice A rationale:

"Kidney stones." Kidney stones are not a common complication of Ankylosing Spondylitis (AS).

While AS primarily affects the spine and joints, it does not directly increase the risk of kidney stones.

Therefore, this choice is not the correct answer.

Choice B rationale:

"Decreased risk of osteoporosis." AS is associated with an increased risk of osteoporosis, not a decreased risk.

The chronic inflammation and reduced mobility associated with AS can contribute to bone loss, making osteoporosis a potential complication.

Choice C rationale:

"Reduced lung capacity." Reduced lung capacity is a known complication of AS.

In severe cases, AS can lead to restrictive lung disease due to the fusion of the ribs to the spine.

This can restrict lung expansion and reduce lung capacity, leading to respiratory issues.

Choice D rationale:

"Improved cardiovascular health." AS itself does not typically lead to improved cardiovascular health.

In fact, chronic inflammation associated with AS may increase the risk of cardiovascular disease.

Therefore, this choice is not the correct answer.