下列离子方程式中，书写正确的是

A．用小苏打治疗胃酸过多：HCO₃^-＋H⁺＝CO₂↑＋H₂O

B．往碳酸钙中滴加稀盐酸：CO₃^2-＋2H⁺＝CO₂↑＋H₂O

C．Na与硫酸铜溶液反应 2Na+Cu²⁺="Cu+" 2Na⁺

D．氢氧化钡溶液与稀硫酸反应：Ba²⁺＋SO₄^2-＋H⁺＋OH^-＝BaSO₄↓＋H₂O

—What's wrong with your ipad2? The sound ____is not clear. 

—Yes. It has been broken for some time. [ ]

A. come out        

B. coming out       

C. to come out      

D. came out