Nitrogen fixation in the root nodules of $Alnus$ is performed by:

Mark the correct sequence of steps for the development of root nodules in legumes:
$a.$ Formation of infection thread.
$b.$ Division of cortical and pericyclic cells.
$c.$ Curling of root hairs.
$d.$ Leghaemoglobin synthesis.

Identify the $A$ to $D$ correctly in the given diagram of root nodule development and choose the correct option accordingly.

In which of the following are root nodules found?

Which plant tissue of the root is responsible for the formation of root nodules in plants of the family $Fabaceae$?

The anaerobic condition for nitrogen fixation is maintained by ..........