I entered Edit Mode, and try to use selection box to drag and select multiple objects, but the selection box can only select some surfaces that facing me, the inside surfaces and the surfaces at the back can not be selected.
What am I doing wrong?
Available selection methods:
The answer of @ObscureGuy was correct, but just to make sure: You can only select mesh parts in Edit Mode, not objects. You can select every part of an object's mesh/data, but technically you cannot select objects.
Alt+Z to enable X-Ray mode. 'Box/Circle/Lasso Select' then picks up everything.