---Excuse me. I’m looking for Be the Best of Yourself.

---Sorry. The book you ask for     out.

A．is selling

B．is sold

C．was selling

D．will be sold

若我厂锅炉的#20钢省煤器管需要进行换管焊接，应采用（）焊条。

A、热307

B、结507

C、热317

D、结422