下列哪种材料是最理想的印模材料()

A．藻酸钾

B．藻酸钠

C．硅橡胶

D．印模膏

E．印模石膏

When ______ help, one often says “Thank you.” or “It’s kind of you.”

A．offering

B．to offer

C．to be offered

D．offered