The distance between stars is measured in . . . . . . .

What is the first step of classification?

Which of the following aspects is an exclusive characteristic of living things?

Find out through internet and popular science articles whether animals other than man have self-consciousness.

The most important characteristic of all living systems is:

$S$ Statement: Reproduction leads to an increase in the number of organisms.
$R$ Reason: In reproduction,organisms produce new individuals similar to themselves upon reaching maturity.
$(a)$ Both $S$ and $R$ are true,and $R$ is the correct explanation of $S$.
$(b)$ Both $S$ and $R$ are true,but $R$ is not the correct explanation of $S$.
$(c)$ $S$ is true and $R$ is false.
$(d)$ $S$ is false and $R$ is true.