Task: Question Answering
Input (English): Problem: the probability of two events a and b are 0.25 and 0.35 respectively . the probability that both a and b occur is 0.15 . the probability that neither a nor b occur is _________ 
Options: a ) 0.55 , b ) 0.4 , c ) 0.5 , d ) 0.05 , e ) 0.6
Output (English): a