The country has already sent up three unmanned spacecraft, the most recent__at the end of last March.

A．has been launched

B．having been launched

C．being launched

D．to be launched

取鱼粉适量放入烧杯中加水煮沸，过滤后的溶液中加几滴稀碘液，如溶液呈蓝色，则说明掺有（）类物质。

A.淀粉

B.石粉

C.贝壳粉

D.皮革粉