The answer is <u>WRECK</u>.
As a noun, 'decay' is the state of gradual damage or decline in strength, soundness, or prosperity, that is to say, of becoming worse. Similar to the noun 'wreck' that is the state of being damaged, disabled, in ruin or dilapidation.
The other words do not support the meaning of 'decay', because 'colossal' refers to something extremely big, 'bare' is something/someone without any clothes or not covered by anything, and 'round' is something shaped like a ball or circle, or curved.
I think this might help you figure out the theme, hope this helps
Make corrections in punctuation and capitalization in the sentences below.

(1) Look at your fingerprints and you will see small ridges in the skin. The pattern of those ridges is different from anyone else’s fingerprints. Fingerprints never change. If the skin were burned off your fingertips time and time again, your fingerprints would be the same as they were once the skin heals.
(2) There are many different characteristics on each fingertip. Each finger has about 100 different marks. No two fingers on the same hand are alike. No two fingerprints have yet been found to be exactly alike.
(3) Everything that is touched by a person carries his fingerprints. Criminals are captured by the police because their fingerprints are found on objects associated with the crime.
(4) The Chinese were the first people to use fingerprinting thousands of years ago. Today, all countries use fingerprints to identify people. The FBI in Washington has a collection of almost 160 million fingerprints.

Answer:
Risk-taking increases between childhood and adolescence as a result of changes around the time of puberty in the brain’s socio-emotional system leading to increased reward-seeking, especially in the presence of peers, fueled mainly by a dramatic remodeling of the brain’s dopaminergic system. Risk-taking declines between adolescence and adulthood because of changes in the brain’s cognitive control system – changes which improve individuals’ capacity for self-regulation. These changes occur across adolescence and young adulthood and are seen in structural and functional changes within the prefrontal cortex and its connections to other brain regions. The differing timetables of these changes make mid-adolescence a time of heightened vulnerability to risky and reckless behavior.