Two students $P$ and $Q$ perform an experiment to verify Ohm's law for a conductor with resistance $R$. They use a current source and a voltmeter with least counts of $0.1 \, mA$ and $0.1 \, mV$,respectively. The plots of the variation of voltage drop $V$ across $R$ with current $I$ for both are shown below. Which statement is most likely to be correct?

• A
  $P$ has only random error$(s)$
• B
  $Q$ has only systematic error$(s)$
• C
  $Q$ has both random and systematic errors
• D
  $P$ has both random and systematic errors