This argument type has been discussed in detail in these three posts:
The posts above cover this argument type in detail.
This questions posed on this argument type are by their very nature are hard to crack. Thus you will encounter such questions only at a higher level. Hence, knowing the algorithm to crack this will come in more than handy on test-day.
Another things to note is that this argument is not only used to posed Strengthen-Weaken questions but also on the Assumption questions. It can also easily be used to a pose a Flawed Reasoning type of question since the answer can be arrived at without the options!
Feel free to use the comments section let me know if you want me to take up and discuss more examples from particular question types.