[racket] evaluate string which contains many definitions

evaluate string which contains many definitions

hello~

I don't know why the following code doesn't working at all

I can eval a-value but not b-func nor c-value

#lang scheme
(require racket/gui)
(require 2htdp/batch-io)
(define-namespace-anchor anchor)
(define ns (namespace-anchor->namespace anchor))
(define content (read-file "./eval.txt"))

(eval (read (open-input-string content)) ns)

(eval 'a-value ns)
(eval '(b-func) ns)
(eval 'c-value ns)


===content of eval.txt===
(define a-value 0)
(define (b-func)
  (* 2 2))
(define c-value 3)
=========================
I expected
0
4
3
as a result but
 reference to an identifier before its definition: b-func
arises
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