The manager should use $2$ suppliers $($option b$)$ to minimize the overall risk and cost. With a $5\%$ probability of a super$-$event affecting all suppliers simultaneously, having two suppliers reduces the likelihood of complete disruption. Additionally, the $10\%$ probability of a unique event affecting one supplier can be better managed with multiple suppliers in place. The cost of managing two suppliers is justified to mitigate the potential $$2,000,000$ financial cost of total disruption. This balanced approach optimizes risk mitigation and cost$-$effectiveness.