Why is $Bt$ toxin not toxic to human beings?

• A
  The toxin recognises only insect-specific targets.
• B
  $Bt$ toxin activation requires a temperature above the human body temperature.
• C
  $Bt$ toxin formation forms a pro-$Bt$ state which requires a $pH$ lower than the one present in the human stomach.
• D
  Conversion of pro-$Bt$ to the active $Bt$ state takes place only in highly alkaline conditions.