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I can't tell you WHICH pieces to use but I can tell you (I think) what they are used FOR and you should be able to find the correct adapter in the pamphlet that normally accompanies the pump (unless you picked it up used).
Two of the adapters are for different sizes of tubing (5/8" and 3/4") that should look about the same. They will fit into the top hole. Pick the one that fits your tubing going back to the tank.
The other piece fits on the front and is used for connecting the pump "in-line" for an out of water arrangement. You don't need it if the pump is to be placed in the sump and I believe it comes with a grid that can be turned to adjust flow if your overflows are a bit slow. We have used this extension to add a sponge to the intake just to keep debris (which should not be in a sump but mine are open so it is just a precaution, putting a sponge on it will also reduce the flow somewhat) from entering the pump.
Looking at the Danner website, their instruction pamphlet may be next to worthless . The closest thing I could find in the manual section was for a Hampton garden pump and I suspect it is the same thing but I does not show a way to determine which adapter is which. It may be marked on the plastic.