sudo certbot -i apache -a manual --preferred-challenges dns \
-d a.example.com -d b.example.com -d c.example.com -d d.example.com \
-d e.example.com -d f.example.com
If you are using DNS validation, you may also choose to just issue a wildcard, which will be less validation steps and work for any subdomain:
sudo certbot -i apache -a manual --preferred-challenges dns \
-d "*.example.com" -d example.com