1) Should there be a failure of both the Elec and Mechanical pumps then the PTU will power the LE Flaps and Slats and Auto slats, using system A pressure but using system B fluid.
2) The alternate flap switch operates the TE devices electricaly, with the switch closing a value to prevent a hydraulic lock and allowing an electric motor to extend/retract the flaps.
If the LE devices were already out you would be stuck with them out since it uses hydraulic power from the standby system via a standby pump to extend only. The TE devices could be retracted but VERY slowly
Hope thats of some help...good luck. who are you off to work for?