Why do classification systems change over time?

Which of the following is not considered an appendage of the skin? nails glands follicles none of the above

Up until 1938, paleontologists accepted the idea that coelacanths (an ancient fish) went extinct at the time that they last appear in the fossil record, about 80 million years ago. but in 1938, a live coelacanth was discovered off the coast of south africa that was compared to the fossil record and found to be the same species what goal of science does this discovery represent

Achild is suffering from fever but the doctor cannot immediately pinpoint the alignment on the basis of this one symptom explain why also mention other two such general symptoms