A 45-year-old patient with ankylosing spondylitis presents with increased thoracic pain and limited chest expansion. Which nursing intervention should be prioritized to improve the patient's respiratory function?

instruct the patient to perform diaphragmatic breathing exercises regularly.

Advise the patient to avoid any physical activity to prevent further pain.

Suggest the use of a lumbar support pillow while sitting

Recommend the patient to increase fluid intake to stay hydrated.