Answer:
c. accidental removal of the parathyroid glands during surgery
Explanation:
Parathyroid gland is found closely situated at the back of the thyroid gland in the human neck region. Regulation of serum calcium levels in the body is a major function of the parathyroid gland through the secretion of a hormone called parathyroid hormone or parathormone.
During the surgery conducted to remove the thyroid gland, it is very likely that the parathyroid glands were accidentally damaged or removed. This most likely led to the non--secretion of parathormone, which is responsible for secretion of calcium in the body, when calcium levels drop.
The answer would be C. Energy is used through the food chain so energy always decreases. Population size would commonly decrease according to the pyramid of food chain but since there's no answer for that, C would be the most suitable
Answer:

point mutation, change within a gene in which one base pair in the DNA sequence is altered. Point mutations are frequently the result of mistakes made during DNA replication, although modification of DNA, such as through exposure to X-rays or to ultraviolet radiation, also can induce point mutations
The answer is D. Seaweed.