Consider the following statements about $Bt$:
$I.$ The bacteria $Bacillus$ $thuringiensis$ $(Bt)$ are used to control butterfly caterpillars.
$II.$ Fresh spores of $Bt$ are mixed with water and sprayed on crops such as brassicas and fruit trees.
$III.$ Insect larvae,after eating these,are killed by the toxin released in their gut.
$IV.$ $Bt$ toxin genes have been introduced into plants to provide resistance to pests.
Which of the statements given above are correct?

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