A letter of guarantee is an irrevocable undertaking by which the issuer holds itself financial liable for the consequences of non-performance of the obligations by the third party toward the beneficial.

A letter of guarantee is an irrevocable undertaking by which the issuer holds itself financial liable for the consequences of non-performance of the obligations by the third party toward the beneficial.

A.担保书是一项不可撤销的保证，发证人对于不履行第三方对受益人义务的后果承担自己的财务责任。

B.担保书是一项不可撤销的保证，发证人对于第三方不履行对受益人的义务承担自己的财务责任。

C.保函是一种不可撤销的承诺，发行人对于不履行第三方对受益人义务的后果承担自己的财务责任。

D.保函是一种不可撤销的，发行人持有本身经济承担的后果不履行义务的第三方受益人的承诺。

正确答案是C