Answer: The DNA double helix is held together by two types of bonds,
covalent and hydrogen.
Explanation: Covalent bonds occur within each linear strand and strongly
bonds the bases, sugar and phosphate groups.
The answer is (b.) ecosystem. An ecosystem is all living organism in an area functioning together with nonliving factors of the environment. An Ecosystem is a community of the living organism that includes the producers, the consumers, and the decomposers.
Answer: It distributes oxygenated blood to the different tissues, it has to be wide enough to fit everything through as efficiently as it can.
essentially its like a tunnel and tunnels have to be wide to fit everything through