Why is $CNG$ considered a better fuel than diesel/petrol?
$I.$ $CNG$ burns most efficiently without leaving any unburnt remnant behind.
$II.$ $CNG$ is cheaper than petrol or diesel.
$III.$ $CNG$ cannot be siphoned off by thieves and adulterated like petrol or diesel.
Which of the statements given above are correct?

• A
  $I$ and $II$
• B
  $I$ and $III$
• C
  $II$ and $III$
• D
  $I, II$ and $III$