Scientists rigorously studied a variety of possible causes, ranging from genetically modified crops to climate change to cell phone towers. How does the use of the word rigorously affect the tone of the excerpt?

4,7

explanation:

being judged by your physical appearance, gender, age or race has been a problem for many people around the world. we all have experienced segregation or rejection at some moment in our life. i   am not the exception. i am an overweight latin girl, two characteristics that do not me very much in a bullying society. i am an excellent student, speak beside my native language – spanish, english and i am currently studying portuguese. once there was a job opening for an international company. i was the perfect candidate for the position. i fulfilled all the requirements to get the job. yes, because of my   curriculum i was called for an interview. the same day, other candidates were appointed too.   i simply said to myself: this is for you, no one else is as prepared as you are, besides, you are smart, honest, responsible and reliable.

the recruiter called me, it was a middle age man, demanding looking one. as soon as he saw me entering the room he looked at me and said: “i am sorry, you are not the type of person we are looking for. it is for the reception and we need someone with different physical appearance”  

i felt like if a train had run over me. i felt miserable. he didn´t even asked me a question nor check on my skills! a pretty face and a perfect body was just as perfect for the position.

when i got home i cried for a long time until my tears dried from my being, then i told myself:   you are who you are, no one can tell you that you are not good enough because of your physical appearance. your intelligence will last forever! bodies age, faces disappear, but you   will always be

i agree, i think a best suits this answer.