Mr Black ____a telephone meeting when I got to his office yesterday afternoon.[ ]

A. has

B. had

C.is having

D. was having

下列物质中，能使紫色石蕊试液变红的是（　　）

A．水

B．稀硫酸

C．碳酸钠溶液

D．氢氧化钡溶液