對于以下代碼：package mainimport "fmt"func emit(c chan string) {    words := []string{"The", "quick", "brown", "fox", "ran", "away"}    for _, word := range words {        fmt.Printf("send %s\n", word)        c <- word    }    fmt.Printf("Close the channel\n")    close(c)}func main() {    wordChannel := make(chan string)    go emit(wordChannel)    word := <-wordChannel    fmt.Printf("receive %s \n", word)    word = <-wordChannel    fmt.Printf("receive %s \n", word)    word = <-wordChannel    fmt.Printf("receive %s \n", word)    word, ok := <-wordChannel    fmt.Printf("receive %s %t\n", word, ok)    word, ok = <-wordChannel    fmt.Printf("receive %s %t\n", word, ok)    word, ok = <-wordChannel    fmt.Printf("receive %s %t\n", word, ok)}下面是輸出：send Thesend quickreceive The receive quick send brownsend foxreceive brown receive fox truesend ransend awayreceive ran truereceive away true為什么發件人 go-routine 不關閉通道？