题目

Most people feel lonely sometimes, but it usually only lasts a few minutes or a few hours. This kind of loneliness is not serious. In fact, it is quite normal. For some people, though, loneliness can last for years. Now researchers say there are three different types of loneliness. The first kind of loneliness is temporary. This is the most common type. It usually disappears quickly and does not require any special attention. The second kind, situational loneliness, is a natural result of a particular situation－for example, the death of a loved one, or moving to a new place. Although this k 函数的定义域是 [　　] A．(3，＋∞) B．(4，＋∞) C．(3，＋∞) D．(4，＋∞)