问题如下：
A combination strategy is constructed as follows:
Long 1 call option at $3, strike price $80,
Short 2 call option each at $4, strike price $90,
Long a call option at $5, strike price $100.
Assume all the options has the same expiration date. If stock price is $105 at At expiration, then strategy will have:
选项：
A.A profit of $1.
B.zero profit.
C.A loss of $1.
D.A profit of $20.
解释：
B is correct.
考点：butterfly spread
解析：这个option的组合可以构成butterfly spread，profit计算方式如下：
Profit = [max{0, (S – XL)} – CL] + [max{0, (S – XH)} – CH] – 2[max{0, (S – XM)} – CM]=max(0, 105– 80)-3+max(0, 105– 100)-5-2[max(0, 105– 90)-4]=0
这题的解题技巧是否可以：因为st=105，组合是看涨期权，都行权。所以，long call k=80亏3块，short call k=90赚8块，long call k=100亏5块。所以total是-3+8-5=0。
