Junk food has become a global culture because it is convenient and you can basically eat it anywhere.
Explanation:
In this modern day and age, people are always busy, no matter what your job/work is. Because of this work environment, maintaining health is not a priority. Just thinking about eating and munching down food is enough for an average person without looking out for the health components of the food. At the end of the day, we want something sweet, something we crave. Health is not a huge motivator in that time frame. Junk food has also been very convenient when it comes to emotional fulfillment. You can just much on it while wallowing in all of your problems and quite frankly, it can be a great companion. Not for your bodily systems though.
In terms of the first question, "They" would be an objective pronoun, but it should be noted that this does not have to be so. for the second, the answer is "my".
