确实是在buyer exercises之后这个OTP才是一个contract。但是seller是不可以不接受buyer行权的。 buyer所要做的就是：
1. Sign the "Acceptance" section in the OTP form (at the bottom half of Page 8)
2. Pay the sellers a deposit amount not exceeding $5,000 which includes the Option Fee
3. Deliver the signed OTP to the sellers within the Option period
2，3找中介作证就可以了。或者用singpost，seller没办法抵赖，因为singpost可以查出信件是否deliver到或者丢失
