d. When a program starts, the value of all three registers is zero. It doesn't support stack and indefinite memory access out of the box either. The virtual machine has 59,049 memory locations that can each hold a ten-trit ternary number, making memory access limited consequently removing possibility of Turing completness. There were attempts to prove Malbolge Unshackled Turing completness. Brainfuck interpreter in Malbolge Unshackled was written to do so. It can be proven using simulation way (which was described in Brainfuck chapter).