a)  To train our minds to remember Krsna always and to leave everything & 
      reside in vrindavan
b)  To train our tongue to speak about Krsna & taste only Krsna Prasad
c)  To reside in Vrindavana & remember Krsna by taking shelter of an advanced
      devotee.
d)  All of the above

The correct answer is
d)  All of the above