Which disease in adults is characterized by the following symptoms: $1.$ Low metabolic rate,$2.$ Increase in body weight,$3.$ Water retention in tissues?

Assertion: Hormone calcitonin has an antagonistic effect to that of parathormone.
Reason: Calcitonin decreases blood calcium level while parathormone increases blood calcium level.

According to pathology,goiter is associated with which of the following?

Tadpoles of a frog can be made to grow into giant-sized tadpoles if they are:

Which of the following radioactive isotopes is used to detect thyroid cancer?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A):$ During pregnancy,the level of thyroxine is increased in the maternal blood.
Reason $(R):$ Pregnancy is characterised by metabolic changes in the mother.
In the light of the above statements,choose the most appropriate answer from the options given below: