下列哪项治疗措施对尖端扭转型室速无效()

A．补充钾盐与镁盐

B．普罗帕酮

C．异丙基肾上腺素

D．β受体阻滞剂

E．心脏起搏

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