Missions to mars are feasible only once every two years ?

Which supports the idea that birds and butterflies both have wings but they do not have a common ancestor with wings? a. the wings are analogous structures that evolved differently and do not have a similar internal structure. b. the wings are homologous structures that evolved differently and do not have a similar internal structure. c. wings of birds are vestigial structures, but the wing structures of bats are not vestigial. d. wings of bats are vestigial structures, but the wing structures of birds are not vestigial

Use the periodic table to determine the electron configuration of dysprosium (dy) and americium (am) in noble-gas notation.

What is the percent by mass of oxygen in fe2o3