The given schematic illustration shows three steps 'P', 'Q' and 'R' of the polymerase chain reaction. Which of the following statements are correct with reference to the illustration given above ?

(i) Step 'P' is showing denaturation at low temperature.

(ii) Step 'Q' is a denaturation of DNA strand at high temperature, followed by annealing.

(iii) Step 'R' is an extension of DNA in presence of thermostable DNA polymerase.

(iv) Step 'Q' is extension with two sets of primers.