How many molecules of sulfur trioxide are present in 1.87 moles of this compound?

The  number  of  molecules  of  sulfur  trioxide  are  present   in  1.87  moles  of  this  compound    is  calculate  using  Avorgadro  law  constant  that  is

1  mole =  6.02  x10^23 moecules
what   about  1.87  moles
  1,87  x  6.02  x10^23 =  1.257  x10^24  molecules

The answer is b because c don't explain why the moths are on them and it isn't a because as we know only one species of moth does this