Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 39 to 43.

Caffeine, as any other drug, can potentially have a disastrous effect on your developing brain and body. The parts of the brain that are in charge of higher functions including the prefrontal cortex and the temporal lobe and, at a young age, these areas are still being developed and refined. 

The reason that caffeine makes you feel alert and less sleepy is because it blocks the action of adenosine, the brain chemical which controls your sleep patterns, and increases adrenaline production, speeds your metabolism. So, get out of the habit of slamming down too many of those high caffeine energy drinks every day; otherwise, you can wave goodbye to good quality sleep and have your brain potentially affected! You can also stop kidding yourself that you're reaching for the caffeine just for the taste because it is tasteless at the levels found in beverages. What you taste is the massive amount of sugar that added to the drink. The caffeine is there to add the kick and to stimulate the production of dopamine in the nucleus accumbens. This is the pleasure and rewarding part of the brain which forms addictions. The upshot is that your brain associates the pleasure of sugar with the stimulation of the caffeine, making you want more. 

(Source: www.ncbi.nlm.nih.gov)

What is the main idea of the passage?