I used to adpat current available AdMob SDK version for new project.
Because it works and I am lazy.
Today I found that AdMob won’t display AD Banner when I adapt old version (7.25.0).
After I download the newest verion (7.27.0) and the AD Banner showed.
Maybe it is the good time for me to think about to use POD to adapt AdMob instead of using STANDALONE sdk download.