---Look! What a nice and clean toilet!   

---Yes. It ______ every morning.

A．is cleaned

B．has been cleaned

C．is being cleaned

D．was cleaned

从思想渊源的角度来看，以下哪一项属于经济学的起源：（）

A、古印度宗教学

B、古希腊家政学

C、古巴比伦建筑学

D、古埃及种植学