下面这段代码输出什么？为什么？

type People interface {
    Speak(string) string
}

type Student struct{}

func (stu *Student) Speak(think string) (talk string) {
    if think == "speak" {
        talk = "speak"
    } else {
        talk = "hi"
    }
    return
}

func main() {
    var peo People = Student{}
    think := "speak"
    fmt.Println(peo.Speak(think))
}

A. speak B. compilation error

B 编译错误 Student does not implement People (Speak method has pointer receiver)，值类型 Student 没有实现接口的 Speak() 方法，而是指针类型 *Student 实现改方法。