There are 30 questions in a certain multiple choice examination paper. Each question has 4 options and exactly one is to be marked by the candidate. Three candidates $A, B, C$ mark each of the 30 questions at random independently. The probability that all the 30 answers of the three students match each other perfectly is
1. $60^{-4}$
2. $30^{-4}$
3. $4^{-30}$
4. $4^{-60}$