I would like to ask you a question about linux Static Routing.

I would like to ask you a question about linux Static Routing-Linux Enterprise Application-Linux server application. The following is a detailed description. When I was learning linux Static Routing, I encountered this problem:

In the Redhat9.0 environment, set the specified CIDR Block route

(1) The online references are as follows:

# Route add-net 192.168.3.0 netmask 255.255.255.0 gw 192.168.6.66

(2) The books on hand are written as follows:
# Route add-net 192.168.3.0 netmask 255.255.255.0 dev eth0
# Route add-net 192.168.3.0 netmask 255.255.255.0 gw 192.168.6.66 dev eth0

(3) another reference book is written as follows:
# Route add-net 192.168.3.0 netmask 255.255.255.0 gw 192.168.6.66
# Route add-net 192.168.3.0 netmask 255.255.255.0 dev eth0
"Gw 192.168.6.66, dev eth0, you can write either of them"
Bytes -------------------------------------------------------------------------------------------------

My problem is:
(1) which of the following statements are correct?
(2) is the "# route add-net 192.168.3.0 netmask 255.255.255.0 gw 192.168.6.66 dev eth0" written in the book correct? If it is correct, can it be abbreviated? How is it true?
(3) On the forum, I found a friend who wrote:
# Route add-net 192.168.3.0 netmask 255.255.255.0 default gw 192.168.6.66

Is this correct? I don't think I need to write default, do I know?