Dan, a financial planner, has always been a big spender and his clients, including Jayce, are used to him picking up the tab. They also know that Dan is frequently hard to contact for weeks at a time. They do not know, however, that Dan has bipolar disorder and swings from manic phases to depressive states. Jayce is one of Dan's longest clients, but he is considering finding another financial planner because of Dan's erratic and unreliable behaviour. Dan can sense that Jayce is frustrated with him, so he offers to buy Jayce's outdated iPhone for $1,000eventhoughthephoneisonlyworth$100. Although he feels bad taking advantage of Dan, Jayce accepts the money. No written evidence of the agreement exists. Is this contract enforceable? 

Yes, because this kind of agreement does not have to be in writing. 

Yes, because Jayce has no way of knowing that Dan is not mentally capable of managing his affairs.

Yes, because Dan needs the phone to communicate with his clients, which is necessary for his work. 

No, because Jayce has sufficient knowledge to suspect from Dan's conduct that Dan lacked the capacity to enter into this contract because of men