How many of the given statements $(i-iv)$ is/are correct?

$i.$ In transcription, adenosine pairs with uracil.

$ii.$ Regulation of lac operon by repressor is referred to as positive regulation.

$iii.$ The human genome has approximately $50,000\; genes.$

$iv. $ Haemophilia is a sex-linked recessive disease.

Select the two correct statements out of the four $(i-iv)$ given below about lac operon.

$i.$ Glucose or galactose may bind with the repressor and inactivate it.

$ii.$ In the absence of lactose, the repressor binds with the operator region.

$iii.$ The z-gene codes for permease.

$iv.$ This was elucidated by Francois Jacob and Jacque Monod.

Operon is

Functioning of structural genes is controlled by

A low level of expression of lac operon occurs at all the time. Can you explain the logic behind this phenomena.