Q. If there are 'M' switches in series numbered from 1, 2,..., M. For circuit to be complete and bulb to glow which of the following is necessary

• 1∧2∧3∧....∧M should be on
• 1∧2∧3∧....∧M should be off
• 1 v 2 v 3 v .... v M should be on
• None of the mentioned

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