Adjacency pairs: adjacent turns that have a close relationship with each other. By this definition, I would classify that example as an adjacency pair. The example I tend to see is
Hello
Hello, how are you?
Adjacency pairs aid fluid conversation, and are usually used to initiate conversation
Question-answer, to my knowledge, is not a term we have to know. But I guess it would be classified as that.
Interrogative tags are something else: questions formed by attaching a "tag" to the end of the statement. For example, "it's cold, isn't it?". They are usually used to confirm that their answer is correct or to hand over the floor.
Also, interesting to note that the "tag" part is often "opposite" to the statement. i.e. If the statement is positive ("it is cold"), the tag is negative ("isn't it"), and vice versa ("he won't call us, will he?")