The nurse is assessing an 8-month-old during a wellness checkup. Which of the following is a normal developmental task for an infant this age

A．Sitting without support.

B．Saying two words.

C．Feeding himself with a spoon.

D．Playing patty-cake.

（）是对象与其外界相互关联的唯一途径。

A、函数调用

B、接口

C、状态转换

D、消息传递