下列反应属于置换反应的是[ ]

A.H₂CO₃==H₂O+CO₂↑

B.4P+5O₂2P₂O₅

C.Zn+H₂SO₄==ZnSO₄+H₂↑

D.HNO₃+NaOH==NaNO₃+H₂O

It was very difficult to rescue the drowning boy in the sea. One moment the rescue workers ____him

but the next moment they _____.    [ ]

A. caught sight of; lost                

B. caught the sight of; lost his sight  

C. caught sight of; lost sight of him      

D. caught the sight of; lost their sight of him