In angiosperms,the functional megaspore develops into which of the following?

If $a, b, c$ are in $AP$,and $b-a, c-b, a$ are in $GP$,then $a: b: c$ is

Boron in green plants assists in

The image formed by a concave mirror of focal length $6 \ cm$ is $3$ times the size of the object. The distance of the object from the mirror is......$cm$.

In flowering plants,senescence is an active cellular process that suggests growth and function. This is best exemplified by:

The number of ways of choosing $10$ objects out of $31$ objects,of which $10$ are identical and the remaining $21$ are distinct,is