The fact of some fraternal twins resembling each other greatly and others looking quite dissimilar highlights an interesting and often overlooked feature of fraternal-twin pairs, namely they vary considerably on a spectrum of genetic relatedness.
a. the fact of some fraternal twins resembling each other greatly and others looking quite dissimilar highlights an interesting and often overlooked feature of fraternal-twin pairs, namely they vary considerably
b. that some fraternal twins resemble each other greatly while others look quite dissimilar highlights an interesting and often overlooked feature of fraternal-twin pairs, namely that they vary considerably
c. with some fraternal twins resembling each other greatly and others looking quite dissimilar, it highlights an interesting and often overlooked feature of fraternal-twin pairs, namely considerable variation
d. with some fraternal twins resembling each other greatly and others looking quite dissimilar, it is a fact that highlights an interesting and often overlooked feature of fraternal-twin pairs, namely a considerable variation
e. because some fraternal twins resemble each other greatly and others look quite dissimilar, this fact highlights an interesting and often overlooked feature of fraternal-twin pairs, namely they vary considerably

The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. the respiratory system does this through breathing. when we breathe, we inhale oxygen and exhale carbon dioxide. this exchange of gases is the respiratory system's means of getting oxygen to the blood.respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. oxygen enters the respiratory system through the mouth and the nose. the oxygen then passes through the larynx (where speech sounds are produced) and the trachea which is a tube that enters the chest cavity. in the chest cavity, the trachea splits into two smaller tubes called the bronchi. each bronchus then divides again forming the bronchial tubes. the bronchial tubes lead directly into the lungs where they divide into many smaller tubes which connect to tiny sacs called alveoli. the average adult's lungs contain about 600 million of these spongy, air-filled sacs that are surrounded by capillaries. the inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. the carbon dioxide follows the same path out of the lungs when you exhale.the diaphragm's job is to pump the carbon dioxide out of the lungs and pull the oxygen into the lungs. the diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. as the diaphragm contracts and relaxes, breathing takes place. when the diaphragm contracts, oxygen is pulled into the lungs. when the diaphragm relaxes, carbon dioxide is pumped out of the lungs. write one paragraph (at least 6 sentences) describing the path of oxygen through the respiratory system. also include why this "order of operations" is the way it is!

How could you find out if that advice is based in scientific evidence?

Why would one lymph node in the neck be swollen and not the other? what causes them to swell?