I believe this is a bit of a trick question, while you are right about both B and D, they both preexist they just develop into other structures. I believe the correct answer is A since the nerve cord is hollow not solid.
It is anatomic dead space
The answer you are looking for is Natural Selection.
Answer:
A star's life cycle is determined by its mass. A star's mass is determined by the amount of matter that is available in its nebula, the giant cloud of gas and dust from which it was born.
The results of the study would be expected to change if the same experiment were repeated with natural gas in the area of a decrease in the reaction time.
<h3>What is Reaction time?</h3>
This is the time frame between when a stimulus and a response or total time taken for a reaction to occur.
Natural gas produces steady amount of heat with a higher temperature which leads to a decrease in reaction time.
Read more about Reaction time here brainly.com/question/1114291