---What do you think of Duan Linxi’s song ?

---I think it’s ________best song in the world. Isn’t it _______ beautiful one?

A．the, the

B．a, a

C．the, a

D．a, the

说明燃烧氧化－非分散红外吸收法中，差减法测定总有机碳的原理。