Assertion ($\mathrm{A}$): Purine always comes opposite to a pyrimidine.
Reason (R): Appropriate uniform distance is maintained between the two strands of the $\mathrm{DNA}$ helix.

A student grew virus in three different media containing ${\mathrm{P}}^{32}, {\mathrm{S}}^{35}$ and DNAase separately and allow this virus to attack to E. coli. The series of observation made by the students are as follows:

a) ${\mathrm{P}}^{32}$ labelled phage particles were produced in E. coli.
b) ${\mathrm{S}}^{35}$ containing phage particles were produced E. coli.
c) Phage particles were observed in E. coli.

d) ${\mathrm{P}}^{32}$ was not observed in phage particles produced by E. coli.
e) ${\mathrm{S}}^{35}$ was not observed in phage particles produced by E. coli.

The correct observations are

Match the following?