为什么string.Replace在Golang中不起作用

I'm making a program to remove the letters from a string if they exsists. But the expected result will not come. The Program I have tried is below:-

package main

import (
  "fmt"
  "strings"
)

func main() {
  strValue := "This is a string"
  stringRemove := []string{"a", "an"}
  var removalString string
  for _, wordToRemove := range stringRemove {
      removalString = strings.Replace(strValue, wordToRemove, "", -1)
  }
  fmt.Println(removalString)
  result := strings.Replace(strValue, " ", "", -1)
  result1 := strings.ToLower(result)
  fmt.Println(result1)
}

Output:-

This is a string
thisisastring

fmt.Println(removalString)

output:-

This is  string
This is a string
This is a string
thisisastring

Expected output:-

thisisstring