4. The shape of a birds wing is the reason they can fly?
Kerosene
Keratin
Krypton
Kudzu
Tobogganing or sledding
Swimming
Floating
Singing
Snowshoeing
Only one
More than five
More than ten
More than twenty
Soft feathers at the bottom of a feather
The stiff hair-like parts of a feather
The central shaft of a feather
None of the above
1
2
3
4
5
6
barbule
shaft
hooklets