Which of the following groups of animals has the most efficient gas exchange?
A: amphibians
B: reptiles
C: birds
D:mammals

What is thought to have caused the mass extinction at the end of the cretaceous period?

Ineed the answer asap. in order to be considered alive, an organism must simultaneously possess the characteristics of homeostasis, heredity, cells, reproduction, and

Transmission electron microscope are best for viewing a) microorganisms in pond water b) internal organs of a mouse c)internal structures of a cell d) surface features of a specimen