Answer:
approximately 4.5 billion years ago
Explanation:
Answer:
T
C
G
A
T
A
Explanation:
Thymine pairs with Adenine.
Guanine pairs with Cytosine.
Environments are always changing so organisms need to adapt to survive. The organisms that survive are the ones that are fit to live in that environment, which is where survival of the fittest comes into play.
A relatively small blood pressure gradient is generally insufficient to move blood through the veins under given conditions, thus venous return must be facilitated by valves within veins and two "pumps." ... As skeletal muscles contract, veins are squeezed to help propel the blood toward the heart.
