An ingredient in marijuana known as THC has been found to inactivate

E does not have any impact on the conclusion. B shows why marijuana will not cause causer even though an ingredient of marijuana can cause cancer. Hence B is correct.

I think the correct answer is B. We need to find an answer that weakens the conclusion 'marijuana causes cancer'.

(A) Several teams of scientists performed the various experiments and all of the teams had similar results. Strengthen. But several is how many? Various too.

(B) The carcinogenic effect of THC could be neutralized by the other ingredients found in marijuana. Correct. The fact that THC could be neutralized by other ingredients can weaken the conclusion that marijuana causes cancer.

(C) When THC kills herpesviruses it weakens the immune system, and it might thus diminish the body's ability to fight other viruses, including viruses linked to cancers. Strengthen.

(D) If chemists modify the structure of THC, THC can be safely incorporated into medications to prevent herpes. Out of scope.

(E) To lessen the undesirable side effects of chemotherapy, the use of marijuana has been recommended for cancer patients who are free of the herpesvirus. Marijuana is introduced to inactivate herpes viruses that can create cancerous cells. So with patients without herpesvirus, we are not sure how marijuana can act. So wrong too.

Although option b is right and i have marked b as correct answer .
Can anyone tell why option D is wrong.

Posted from my mobile device

Hi samguru68, Welcome to GMAT Club!

So the conclusion of the argument claims that (in a gist) "Cannabis is causing cancer" and we want to weaken this conclusion.

Option D talks about a futuristic possibility - "if scientists does something, we can prevent something..." This cannot be used an a strong weakener as it does nothing to the conclusion that has been made about existing cannabis causing cancer.

This is why a more direct option is B, which talks about other chemicals in cannabis that prevent cancer right NOW in the present.

Does this make sense?

One thing I dont like about answer B is "could be", not assertive enough, even though it is the best choice.

Marijuana contains THC.
THC inactivates herpesviruses.
Inactivated herpesviruses makes cancer cells.
So, Marijuana causes cancer.

Weaken the argument.

(A) Several teams of scientists performed the various experiments and all of the teams had similar results. - Strengthens.
(B) The carcinogenic effect of THC could be neutralized by the other ingredients found in marijuana. -
Let's modify the statements above,

Marijuana contains THC and XYZ.
THC inactivates herpesviruses.
Inactivated herpesviruses makes cancer cells.
XYZ prevents inactivated herpesviruses from making cancer cells.
So, Marijuana DOES NOT cause cancer.

(C) When THC kills herpesviruses it weakens the immune system, and it might thus diminish the body's ability to fight other viruses, including viruses linked to cancers. - Says immunity is weakened so that body cannot fight cancer cells, which worsens the problem and strengthens that weed can cause cancer.
(D) If chemists modify the structure of THC, THC can be safely incorporated into medications to prevent herpes. - What can be done to prevent herpes is irrelevant.
(E) To lessen the undesirable side effects of chemotherapy, the use of marijuana has been recommended for cancer patients who are free of the herpesvirus. - lessening effects of chemotherapy is irrelevant here.