In heart cells,which molecule acts as a second messenger and increases the contraction of muscle cells in response to adrenaline?

In the mechanism of hormone action,which of the following is $NOT$ a second messenger?

Which one of the following pairs of hormones are the examples of those that can easily pass through the cell membrane of the target cell and bind to a receptor inside it (mostly in the nucleus)?

Which of the following is an example of negative feedback control in humans?

Which of the following statements are applicable to hormones?
$I -$ Neural messengers
$II -$ Intercellular messengers
$III -$ Produced in trace amounts
$IV -$ Nutrient chemicals
$V -$ Released into the blood after production.

Identify $A, B$ and $C$ in the diagrammatic representation of the mechanism of hormone action.
Select the correct option from the following: