The human cardiovascular system is considered closed because
a. blood is continuously circulated in the body.
b. blood provides nutrients to organs.
c. blood collects oxygen from the lungs
d. there are no holes for blood to enter or leave the system

The embryos of a bird, a reptile, and a mammal are similar in appearance. how does comparing the physical appearance of embryos of different species support the theory of evolution? a. it shows that these organisms share a common ancestor. b. it provides evidence that these organisms eat the same foods.c. it shows that these organisms share the same habitat.d. it provides evidence that these organisms suffered a genetic mutation.