What is mutual life insurance converted to stock via former employer considered for how I acquired stock?

I have a 1099B from sale of stock. I acquired the stock from my previous employer back in 2001. It originally was obtained by a Mutual Life Insurance conversion to stock. The original cost per share when it went public was $18.50. The cost basis is $0 from my understanding on my form and calling Computershare. My question is, Turbotax is asking me how I acquired the stock. The options are ESPP, NQSO, ISO, RS, RSU, Mutual Funds, and Bonds or other. What option do I choose? I know it could impact the amount of the stock taxed. If other, it appears it will take a big chunk out of my return. Thanks