I may be overthinking this one. Heres my summary. Let me know if it makes sense or is helpful to you.

The argument is basically the doctor vs. the dietary researcher. The researcher is saying the doctors conclusion is invalid. So what is the doctors conclusion?

The doctors argument in concise terms

Rat study summary: rats on a diet live longer than rats not on diet

Doctors conclusion in response to study: North Americans on a diet will live longer

Doctors conclusion requires following assumption: study valid for rats → study valid for humans

Dietary researcher argument

Conclusion: doctor conclusion not supported by study, since N. Americans are not similar to lab rats.

Basically her assumption is: studies valid for lab rats are not valid for humans

Why?

Because lab rats eat more than native rats

Her assumption: North Americans are like native rats but study addresses lab rats

While doctor assumption is lab rats are similar enough to North americans to be valid.

Answer choice A hurts the dietary researchers argument since North Americans are overweight the dietary researcher's assumption that N. Americans are not similar to lab rats is invalid. Since they are more similar to lab rats than native rats when answer A is added

sounds to me like you've made tremendous progress going from 35 minutes to 9-14 minutes. I would keep doing the problems over and over until the timing you want becomes second nature. If you've made that much progress then you'll likely keep improving with practice.

I completely misread last sentence. It makes perfect sense now. At first I read it as if you have a back injury then drugs are necessary which made no sense but last sentence states as sufficient condition Back Injury & Receive the drug→ Drug necessary If they didn't receive it then its not necessary. I incorrectly assumed all back injuries needed the drug from the statement when it says only those who received the drug needed the drug.