With the development of science, more new technology ______to the field of IT.

A．has introduced

B．is being introduced

C．is introduced

D．was introduced

两台离心泵的流量、扬程分别用Q₁、H₁和Q₂、H₂表示，当它们串联工作时，则流量满足Q_总=Q₁=Q₂，扬程应满足（）。

A、H_总=H₁－H₂

B、H_总=H₂－H₁

C、H_总=H₁=H₂

D、H_总=H₁＋H₂