As covalent bonds are strong it makes the sugar phosphate backbone a stable molecule which will HV less chances for a mutation while the huydrogen bonds exist for the ease of DNA replication as they are strong in a way but weak for the replication to take place easily.
I believe it is the retina that changes shape to focus on distant objects.
Hydrogen (62.9%), oxygen (almost 24%), carbon (nearly 12%), nitrogen (nearly 0.6%), calcium (0.24%) and phosphorus (0.14%).
The point on earth's surface directly above an earthquakes focus (hypocenter) is called the epicenter.
The answer would be C valleys formed by a glaciers.
