Choose all of the characteristics from the list below that are examples of adaptations common among all birds.
(1) backbone
(2) cold-blooded
(3) give live birth to offspring
(4) sharp teeth
(5) solid bones
(6) four legs or feet
(7) feathers
(8) hollow bones
(9) warm-blooded
(10) four-chambered heart
(11) lay hard-shelled eggs
(12) two legs or feet
(13) soft-shelled eggs
(14) two-chambered heart