When ever we change all final states to non final and all non final to final states ,then we get the complement of the DFA.And in case of DFA the language accepted by the complement DFA is the complement of the language accepted by the actual DFA.
So M here accepting language L. And the complement DFA M1 will accepts language L1.Now as per above statement L1 is complement of L.
So L1=L' =(0+1)*-L // Assuming that language is defined over 0,1.
So a is correct answer here.
Remeber that this does not hold true in NFA.It will hold in NFA only if that NFA is a DFA.