what's the relationship between sd-dbus && dbus-daemon?

Question

I am confused recently about sd-dbus && dbus-daemon.

In this blog: http://0pointer.net/blog/the-new-sd-bus-api-of-systemd.html

lenart says from v221 release of systemd use sd-dbus API

I read some blogs and get a result , but do not know is it correct?

Q1:

there are 3 kinds of dbus libarys

1. libdbus
2. GDbus
3. sdbus

Is it correct ?

Q2:

we konw dbus-daemon is based on libdbus .

But we know systemd have a dbus-daemon also ? why lenart says systemd is based on sd-dbus but not libdbus?

Q3:

lenart says after v221 release of systemd use sd-dbus API, But I see before v221 there are sd-dbus in source code also ,that's why ?