If it has valves then it is a vein.
Savannah is the answer you are looking for here.
<span>Having standard written research protocols is the correct answer. ;)</span>
The answer is D
One way to remember this is when you are building a bridge there is one piece right in the middle that keeps the whole thing from collapsing that is called the key-stone. If a keystone species goes extinct then the rest of the ecosystem will crumble around it.
Answer:
D
Explanation:
the circulatory absorbs nutrients and carries the chemical to signal through endocrine to control the speed of digestion.
