Oil is currently trading at $100. You want to buy oil and store it for 1 year and then sell it at t = 1.  Assume the risk free rate is 5% (annual rate with annual compounding). The options below are  European with 1 year to maturity. 
a) Describe how you can construct a synthetic long oil position (ignore the storage cost) using a  Call with K = 90, a Put with K = 90, and the risk free asset. 
b) Now assume the 1-year storage cost is $1, payable at t = 0. Suppose the price of a K = 90 Put  is $20.
What is the highest value of a K = 90 Call such that there is no arbitrage? 
c) Suppose the price of the call were $0.10 greater than your answer to part. Describe how you would construct an arbitrage strategy?