1. An apparatus of plural charged particle beams, comprising: a specimen stage, which sustains a specimen thereon; and multiple sub-columns, which are placed above an observed surface of said specimen and respectively perform one of multiple functions for observing said observed surface, wherein a first function of said multiple functions is high-throughput inspection of interested features on said observed surface, and a second function of said multiple functions is high-resolution review of said interested features on said observed surface, wherein each of said multiple sub-columns comprises: a gun unit, which comprises a charged particle source and a condenser lens to provide a primary charged particle beam along an optical axis of said each sub-column; and an imaging system, which comprises a beam-limit aperture, an objective lens, a deflection scanning device and a first charged-particle detector, wherein said beam-limit aperture and said objective lens are aligned with said optical axis, said beam-limit aperture limits a current of said primary charged particle beam to a desired value, said objective lens focuses said primary charged particle beam onto said observed surface, said first charged-particle detector detects secondary charged particles emitted from said observed surface where said primary charged particle beam impinges, and said deflection scanning device deflects said primary charged particle beam to scan said observed surface so that an image of said observed surface can be obtained, wherein said objective lens comprises a magnetic objective lens, wherein said magnetic objective lenses of said multiple sub-columns are formed by a multi-axis magnetic objective lens which comprises: an upper magnetic conductor plate with multiple upper through holes and a lower magnetic conductor plate with multiple lower through round holes, both of which are parallel to each other, wherein each of said multiple upper through holes is aligned with one of said multiple lower through round holes and both are aligned with said optical axis of one of said multiple sub-columns and form a pair of through holes, multiple upper magnetic round rings, which are respectively inside and aligned with upper through holes of said pairs of through holes with first radial gaps therebetween, and extend downward through inside said lower through round holes of said pairs of through holes to form first non-magnetic gaps therebetween, wherein said first radial gaps can be vacuum or filled of non-magnetic or weakly-magnetic material, and a common excitation coil located between said upper magnetic conductor plate and said lower magnetic conductor plate to provide a common magnetic flux, thereby forming multiple magnetic objective sub-lenses respectively configured by said multiple pairs of through holes and said upper magnetic round rings therein, wherein said first non-magnetic gaps perform as magnetic-circuit gaps of said multiple magnetic objective sub-lenses respectively, wherein each of said magnetic objective lenses is one of said multiple magnetic objective sub-lenses, and said magnetic objective sub-lenses inside said sub-columns performing different functions are different in geometric shape.