Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Poles parts of the planet does solar energy have difficulty reaching.
What parts of the planet does solar energy have difficulty reaching?

Chordates include vertebrates and invertebrates that have a notochord.
Chordates include vertebrates and invertebrates that have what?

Smaller surface area does a large log burn relatively slowly compared to the same mass of wood in the form of small twigs.

Why does a large log burn relatively slowly compared to the same mass of wood in the form of small twigs?