Consider the following statements:
$I.$ Ladybirds and dragonflies are used to get rid of aphids and mosquitoes.
$II.$ The bacteria $Bacillus$ $thuringiensis$ $(Bt)$ are used to control butterfly caterpillars.
$III.$ $Trichoderma$ $sp.$,free-living fungi,are present in root ecosystems where they act against several plant pathogens.
$IV.$ $Rhizobium$ is a symbiotic bacterium that lives in the stem of legumes.
Which of the statements given above are correct?

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