Answer:
A. The first reason that teen brains are more sensitive to junk food is that they are still developing the ability to assess risks and control actions.
Step-by-step explanation:
The sentence supporting the conclusion that teenager's brains change over time is the first sentence from the selection.
The first sentence provides some context clues such as the word "developing." This word can be associated with the phrase, "change over time." To develop is to become more mature, which is definitely a change. This means that the reason for the change relies on the development of the teenager's ability to assess risks and control his/her actions, which means when they get older, they become more capable of choosing healthier options.
Choices B, C and D do not provide any support regarding the development of the brain. They only state some facts regarding the function of the prefrontal cortex and which part of the brain the change occurs.