Which of the following is/are undecidable?
- AGiven two Turing machines M1 and M2, decide if L(M1) = L(M2).
- BGiven a Turing machine M, decide if L(M) is regular.
- CGiven a Turing machine M, decide if M accepts all strings.
- DGiven a Turing machine M, decide if M takes more than 1073 steps on every string.
✓ Correct answer: A
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