problem in lab 6.2

hi there, I'm trying to do part 2 and 3 of the DNS labs on a google cloud VM instance running Centos stream 8 (because I scheduled the LFCS exam with that OS). And I' m getting this error:

/etc/named.conf:61: 'primary' unexpected

when typing this command:

[root@instance-1-centos-3 student]# named-checkconf -z

after adding this stanza:
zone "example.com." IN {
type primary;
file "/etc/bind/example.com.zone";
};

I tried using master as well. it passed the check , but when doing the service restart, it throws an error. I added the next stanza, and the result is the same. Can anybody help please?

journalctl -xe

-- The start-up result is done.
Sep 01 20:10:27 instance-1-centos-3 systemd[1]: Starting Berkeley Internet Name Domain (DNS)...
-- Subject: Unit named.service has begun start-up
-- Defined-By: systemd

-- Support: https://access.redhat.com/support

-- Unit named.service has begun starting up.
Sep 01 20:10:27 instance-1-centos-3 bash[12348]: /etc/named.conf:61: 'primary' unexpected
Sep 01 20:10:27 instance-1-centos-3 systemd[1]: named.service: Control process exited, code=exited status>
Sep 01 20:10:27 instance-1-centos-3 systemd[1]: named.service: Failed with result 'exit-code'.
-- Subject: Unit failed
-- Defined-By: systemd

-- Support: https://access.redhat.com/support

-- The unit named.service has entered the 'failed' state with result 'exit-code'.
Sep 01 20:10:27 instance-1-centos-3 systemd[1]: Failed to start Berkeley Internet Name Domain (DNS).
-- Subject: Unit named.service has failed
-- Defined-By: systemd

-- Support: https://access.redhat.com/support

-- Unit named.service has failed.

-- The result is failed.

This is my named.conf file:

//
// named.conf
//
// Provided by Red Hat bind package to configure the ISC BIND named(8) DNS
// server as a caching only nameserver (as a localhost DNS resolver only).
//
// See /usr/share/doc/bind*/sample/ for example named configuration files.
//

options {
// listen-on port 53 { 127.0.0.1; };
listen-on port 53 { any; };
listen-on-v6 port 53 { ::1; };
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
secroots-file "/var/named/data/named.secroots";
recursing-file "/var/named/data/named.recursing";
// allow-query { localhost; };
allow-query { any; };

/* 
 - If you are building an AUTHORITATIVE DNS server, do NOT enable recursion.
 - If you are building a RECURSIVE (caching) DNS server, you need to enable 
   recursion. 
 - If your recursive DNS server has a public IP address, you MUST enable access 
   control to limit queries to your legitimate users. Failing to do so will
   cause your server to become part of large scale DNS amplification 
   attacks. Implementing BCP38 within your network would greatly
   reduce such attack surface 
*/
recursion yes;
 
dnssec-enable yes;
dnssec-validation yes;
 
managed-keys-directory "/var/named/dynamic";
 
pid-file "/run/named/named.pid";
session-keyfile "/run/named/session.key";
 
/* https://fedoraproject.org/wiki/Changes/CryptoPolicy */
include "/etc/crypto-policies/back-ends/bind.config";

};

logging {
channel default_debug {
file "data/named.run";
severity dynamic;
};
};

zone "." IN {
type hint;
file "named.ca";
};

zone "example.com" IN {
type primary;
file "example.com.zone";
};

zone "45.20.10.in-addr.arpa." IN {
type primary;
file "45.20.10.in-addr.arpa.zone";
};

include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";

and these are my zone files:

----example.com

$TTL 30
@ IN SOA localhost. admin.example.com. (
2012092901 ; serial YYYYMMDDRR format
3H ; refresh
1H ; retry
2H ; expire
1M) ; neg ttl
IN NS localhost.;
www.example.com. IN A 192.168.111.45
www.example.com. IN AAAA fe80::22c9:d0ff:1ecd:c0ef
foo.example.com. IN A 192.168.121.11
bar.example.com. IN CNAME www.example.com.
;generate one hundred entries host1 thru host100
$GENERATE 1-100 host$.example.com. IN A 10.20.45.$

-----45.20.10.in-addr.arpa

$TTL 30
@ IN SOA localhost. admin.example.com. (
2012092901 ; serial YYYYMMDDRR format
3H ; refresh
1H ; retry
2H ; expire
1M) ; neg ttl
@ IN NS localhost.;
;generate 1-254
$GENERATE 1-254 $ IN PTR host$.example.com.111

info about my os, cat /etc/os-release

NAME="CentOS Stream"
VERSION="8"
ID="centos"
ID_LIKE="rhel fedora"
VERSION_ID="8"
PLATFORM_ID="platform:el8"
PRETTY_NAME="CentOS Stream 8"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:centos:centos:8"
HOME_URL="https://centos.org/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_SUPPORT_PRODUCT="Red Hat Enterprise Linux 8"
REDHAT_SUPPORT_PRODUCT_VERSION="CentOS Stream"