in u3d ,where is "Expert Mode",how find it ?

6.Only member variables are serialized and are shown in the Inspector.

Private and protected member variables are shown only in Expert Mode. Properties are not serialized or shown in the inspector.

where is "Expert Mode",how find it ?

When it says "Expert" it means "Debug." I've filed a bug report on this documentation so it will hopefully be fixed in the future, but in order to do what the current documentation says, click the button on the far right of the inspector tab that looks like a downward facing arrow and three horizontal lines. From the dropdown menu there, select "Debug" and you'll be in "Expert Mode"