That's a component of a phospholipid, which is a lipid.
The right answer is C. I think, a. and d. are obviously not serious. B is not true, because Ag and Au are in the same group in the periodic table and therefore have the same number of electrons in the last level. So, they form ions with the same charge. C is true beacause Ag and Au have different numbers in the periodic table and different amount of protons and neutrons in their nucleuses.
They may have ran out of oxygen, or they may not have been water dwelling snails, as not all are, lack of food, no flow of water into and out of the tank would cause them to run out of oxygen.
Upon inhalation, the diaphragm contracts and flattens and the chest cavity enlarges. This contraction creates a vacuum, which pulls air into the lungs.
