PLEASE HURRY, WILL GIVE BRAINLY TO CORRECT ANSWER!

which of the following makes it difficult to reach and explore the outer planets?
1. the surfaces are too icy and slippery to land on.
2. they contain a lot of helium in their atmospheres.
3. massive storms with fast winds cover the surfaces.
4. none of the above.
5. both 1 and 2
6. both 2 and 3.