. Charles, a single 55-year-old CEO of a technology start-up company, earns a $2 million base salary with a $400,000 bonus. He is not a participant in any retirement plans at work. What is the maximum deductible IRA contribution Charles can make for the 2018 tax year?

a. $0.

b. $1,000.

c. $4,000.

d. $5,500.

e. $6,500.