The primary function of the thyroid gland is to regulate..........

On an educational trip to Uttaranchal,Ketki and her friends observe that many local people have swollen necks. Please help Ketki and her friends to find out the solutions to the following questions.
$(a)$ Which probable disease are these people suffering from?
$(b)$ How is it caused?
$(c)$ What effect does this condition have on pregnancy?

Symptoms like pot-bellied,pigeon-like chest,protruding tongue,and mental retardation are characteristic of:

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:

Which gland is responsible for maintaining the basal metabolic rate $(BMR)$?

Which substance is responsible for metamorphosis in amphibians?