What special feature allows birds to fly?

Instead of heavy jaws and teeth, they have lightweight beaks. And instead of fur, they have feathers. These are light, streamlined and cleverly adjustable for flight control. Their bones are also hollow (pneumatised) making them lighter for flight.

Explanation:

lol its to easy and almost common sense

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

it is because according to the process , scientific inquiry is a process with many steps because each step occurs to the scientist and if you just skip a step there would be no steps to scientific inquiry.