Underwater living faces many of the same life support challenges as living in space. ... But in the future, underwater habitats might provide their own oxygen with artificial gill technology to extract dissolved air from the sea water
Since humans do not have gills, we cannot extract oxygen from water. Some marine mammals, like whales and dolphins, do live in water, but they don't breathe it. They have developed a mechanism to hold their breath for long periods of time underwater.
To put these depths into perspective, three American football fields laid end to end would measure 900 feet (274.32 m) long — less than the distance these divers reached underwater. Most recreational scuba divers only dive as deep as 130 feet (40 meters), according to the Professional Association of Diving Instructors.
The term that is used to describe a chemical reaction in which water is produced or gained I believe is Dehydration Synthesis.
The most true answer from these choices is:
Methyl groups most often added to guanine-cytosine base pairs because they are held by three hydrogen bonds, and this decreases the probability of gene expression.
I think it's called the Acrosome
