Used Car Commission

Used Car Commission.William promised to sell Helen's car for her,but he wanted a commission of 10%.Helen signed an instrument promising to pay William a 10% commission if he sold her car.William assigned the agreement to Phil.Helen's car was sold and the buyer paid Helen.A dispute ensued between Helen and William regarding whether William found the buyer or the buyer found Helen.When Phil asked Helen for payment on the instrument,Helen refused.William,Helen,and Phil settled their dispute without going to court,and Helen wrote Phil a check for $3,000.Phil endorsed the check on the back,planning to take it to the bank the next day.Unfortunately,Phil lost the check and it was found by Barry,who cashed it at the local bank.Barry then left town.Which of the following is true regarding the instrument signed by Helen promising to pay William a 10% commission if he sold her car?

A) The instrument is negotiable.
B) The instrument is not negotiable,but only because it is based on a condition.
C) The instrument is not negotiable,but only because Helen is not a merchant.
D) The instrument is not negotiable,but only because it is not for a sum certain.
E) The instrument is not negotiable because it is based on a condition and also because it is not for a sum certain.