It was in time of danger       he made the final decision       they should send more doctors there.       

A．that ;that

B．when; which

C．where ;what

D．where;that

下列物质中，不能够直接证明稀硫酸是酸性溶液的是（）

A．pH试纸

B．无色酚酞试液

C．紫色石蕊试液

D．氢氧化铜