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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def controlled(self, control_qubit):
 """ Add the CONTROLLED modifier to the gate with the given control qubit. """

        control_qubit = unpack_qubit(control_qubit)

        self.modifiers.insert(0, "CONTROLLED")
        self.qubits.insert(0, control_qubit)

        return self