七叶苷水解试验中，七叶素与下列何离子反应其培养基变黑的是

A．Fe²⁺
B．Fe³⁺
C．Cu²⁺
D．Mg²⁺
E．Zn²⁺

汉译英：“承兑交单；付款交单；货到即付”，正确的翻译为：( )

A．document against acceptance；document against payment；payment against arrival

B．document against payment；document against acceptance；payment against arrival

C．document against acceptance；payment against arrival；document against payment

D．payment against arrival；document against payment；document against acceptance