Suppose a stock is priced at 100. Each of the next two periods it will either go up 10% or fall 10%. The simple, one-period risk-free rate is 2%. What is the price of the two-period butterfly on the stock, which is long two-period calls struck at 90 and 110, and short two two-period calls struck at 100?

a.

$4.33.

b.

$4.15.

c.

$4.24.

d.

$4.41.