大量的野生生物价值还未开发，这些生物也许在提取药物、改良品种等方面有重要作用，这体现了生物多样的 [ ]

A．潜在价值    

B．直接价值      

C．间接价值    

D．无价值

— It’s very kind           Betty to give us a hand.

— That’s true. We should thank her           helping us out.

A．for; for

B．of; for

C．for; of

D．of; of