A client on an inpatient psychiatric unit at a community mental health center is pacing the hallway and appears agitated. When the nurse approaches him, he says loudly, "Leave me alone. " What's the nurse's best approach ？（）

A．Say nothing and pace with the client.

B．Say "You sound upset. I'd like to help. "

C．Say "okay" and walk away.

D．Summon help in case the client becomes aggressive.

将SO₂通入BaCl₂溶液中至饱和未见有沉淀生成，继续加入另一物质，仍无沉淀生成，则该物质可能为（　　）

A．Cl₂

B．NH₃

C．H₂SO₄

D．HCl