An angry science student drops his textbook out of a second story window. Why does it fall to the ground? You may choose more than one response.

A. The net force acting on the book by gravity is down.
B The drag force of the air pulls it down.
The student let the book go, removing the force of his hand.
D There is a strong magnetic force between the book and the ground.

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

The number to the right of an element's symbol (ex. c-12) identifies the of an isotope.

What two factors can affect the properties of a hydrocarbon? a. the number of its carbon atoms and the number of single bonds b. the number of its carbon atoms and the arrangement of its atoms c. the arrangement of its atoms and the number of its double bonds