Julie Was Diagnosed with an Aggressive Tumor of the Thyroid

Julie was diagnosed with an aggressive tumor of the thyroid. Surgery was performed to remove the thyroid. However, post-operatively, Julie's blood Ca²⁺ levels began declining to life-threatening levels. This decline is most likely due to

A) thyroid hormone replacement therapy after the surgery.
B) damage to the anterior pituitary during surgery.
C) accidental removal of the parathyroid glands during surgery.
D) improper laboratory handling of blood samples.
E) post-traumatic stress disorder.