Object-oriented analysis (OOA) is a semiformal specification technique for the object-oriented paradigm. Object-oriented analysis consists of three steps. The first step is（）. It determines how the various results are computed by the product and presents this information in the form of a（） . and associated scenarios. The second is （）, which determines the classes and their attributes; Then determine the interrelationships and interaction among the classes. The last step is （）, which determines the actions performed by or to each class or subclass and presents this information in the form of（） .

which determines the actions performed by or to each class or subclass and presents this information in the form of（） .

A.activity diagram

B.component diagram

C.sequence diagram

D.state diagram

化学用语是学习化学的主要工具．请根据要求填空．

（1）空气中含量最多的气体是______．（填写化学式）

（2）该气体会引起温室效应，并且又是光合作用的主要原料之一，该气体是：______．（填写化学式）

（3）写出五氧化二磷的化学式并标出磷元素的化合价______．

（4）写出工业上用石灰石制取生石灰的化学方程式：______．