ATPL: A directional gyro is:1- a gyroscope free around two axis 2- a gyroscope free around one axis3- capable of self-orientation around an earth-tied direction 4- incapable of self-orientation around an earth-tied directionThe combination which regroups all of the correct statements is:NB: the degree(s) of freedom of a gyro does not take into account its rotor spin axis.