Explain: Cockroach is harmful for human beings.

Which of the following statement$(s)$ is/are correct regarding cockroaches?
$(i)$ The body of the cockroach is segmented and divisible into three distinct regions - head,thorax and abdomen.
$(ii)$ Blood vascular system is of closed type.
$(iii)$ They are monoecious and both sexes have well developed reproductive organs.
$(iv)$ The development of $P. americana$ is paurometabolous,meaning there is development through nymphal stage.

$RBC$ are not found in .......

Number of segments found in the body of an adult cockroach is

Periplaneta differs from Blatta in

The characteristic feature that distinguishes between male and female cockroaches is .........