I really appreciate ____ to help me with my maths, but I’m afraid that I have no time this week．

A．you to offer

B．it you offer

C．your offering

D．this you are offering

两栖动物的含义：幼体生活在水中，用鳃呼吸；成体生活在水、陆环境中，用肺呼吸，用（）辅助呼吸。