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. $4^{-60}$