—Look! There is         beautiful rainbow in the sky．

—Take the books for me, I’d like to take a photo of     rainbow before it disappears．

A．a; the

B．the; a

C．the; the

D．a; a

鉴别下列各组物质，选用的方法或试剂不正确的是

A．A

B．B

C．C

D．D