地图范围循环中的空接口

The Below code is not working as expected.

package main

import "fmt"

func main() {
  questions := make(map[int]interface{})
  questions[1] = map[interface{}]string{
    "q1": "This is Question - 1?",
    "op1": "This is Option - 1",
    "op2": "This is Option - 2",
    true: "This is Option - 1",
  }

  // This give map[interface {}]string
  fmt.Printf("%T 
", questions[1])

  // This not working
  for key, val := range questions[1] {
    printf("%v : %v", key, val)
  }


}

The for loop that is ranging over the map is not working.

The Go compiler giving error "Cannot range over questions[1] (type interface {})"

make go understand questions[1] have type is map

for key, val := range questions[1].(map[interface{}]string) {
    fmt.Printf("%v : %v
", key, val)
}