Explain whether each of the following transactions results in a valid negotiation:

a. Arnold gives a negotiable check payable to bearer to Betsy without indorsing it.

b. Golden indorses a negotiable promissory note payable to the order of Golden, ‘‘Pay to Chambers and Rambis, (signed) Golden.''

c. Porter lost a negotiable check payable to his order. Kersey found it and indorsed the back of the check as follows: ‘‘Pay to Drexler, (signed) Kersey.''

d. Thomas indorsed a negotiable promissory note payable to the order of Thomas, ‘‘(signed) Thomas,'' and delivered it to Sally. Sally then wrote above Thomas's signature, ‘‘Pay to Sally.''