根据句意，写出括号内所给单词的适当形式。

小题1:Many of my friends were invited to the party last Sunday because of my _________ ( twenty ) birthday. 

小题2:Boys, don’t touch the machines, or you may hurt _________ ( you ). 

小题3:The International Union Against Cancer says about seven hundred million children _________ ( breath ) smoke-filled air. 

小题4:I can’t understand his             (silent) on such an important matter.

研究的成果往往为各级教育行政部门决策和教育工作者提供有用的信息的是（）

A．基础研究

B．应用研究

C．发展性研究

D．预测研究