There are many possibilities of strengthening the argument:

1. Identifying and strengthening an assumption underlying the conclusion
2. Strengthening or validating the conclusion itself
3. Ruling out alternative explanations - an answer choice can strengthen by saying that a potential "weakener" is NOT true
4. Citing similar cases in which the conclusion holds

Thank you Mastergmat.
The case 3 and 4 , in fact , is the case 1. is that right?

Another point which is more important

regarding case 1 and 2 in your list, if case 1 and case 2 are different, there will be

a new information which increase belief in the conclusion but not increase belief in an assumption.

pls, give us one examle of the case.

if the new information which increase belief in the conclusion must increases belief in an assumption, case 1 and case 2 are the same.

of course, there is one case more. The assumption must be an strengthener.

Thank you. pls, help.

Anyone, pls, give an example of strengthening problem in which a strengthener validate the conclusion ifself (the case 2 above)

most of the cases, I see that a strengtheners validate an assumption of the conclusion. I do not know of the strengthener which validates the conclustion itself.

duongthang wrote:Anyone, pls, give an example of strengthening problem in which a strengthener validate the conclusion ifself (the case 2 above)

most of the cases, I see that a strengtheners validate an assumption of the conclusion. I do not know of the strengthener which validates the conclustion itself.

Giving an example of the situation mentioned above or an analogy - perfect for strengthening!