the case could also be that ellen wrongly diagnosed the disease as measles.
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That would be out of scope.
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PS: Correct me if I am wrong.

one more thing: the question does not ask us to take the above statements (comments by the speakers) as true. It only assumes that "nobody who has measles is fine."
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"wannabe trick" question....bet the real test wont have anything this contentious

I fell for C too...there is a possibility that they are both wrong because Shirley's children have some other illness, therefore:

All three of Shirley's children DON'T have the measles!
As a matter of fact, all three of Shirley's children are NOT fine!

E - Win
L - Lose

E - Win
L - Win

E - Lose
L - Win

E - Lose
L - Lose

Which of the following must be true? Actually with the given information we can only predict both are wrong. We don't have enough information to predict the others. The first scenario is ruled out by assumption.

Is it really necessary that there can be only person with the name Sherlie.?
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This question is a real pain in the rear. I picked C at first, but I believe it is B based on what other members have said.

It is possible that the children do not have measles, they could be sick with something else.. Or two could have measles, one is fine.. etc. (Thus, we cannot make the blanket statement about all 3) Therefore, we cannot say that either Lois or Ellen must be correct. It is possible that both are wrong - B.

B for me too! Interesting question.

Both can be wrong as the discussion is about three children. If only one or maximum two of them have measles, then both are wrong since both the statements are about "all three".

Basically, in all cases in which all three are not in the same condition, both the statements would be incorrect.

Hope this helps.

I went with option C and here is the explanation for my choice. I'll strict my explanation to only option B and C, since the discussions so far are only on these 2 options.

Let me start with my reason for rejection of option B:

The question says based on X assumption, which of the following must be true?

Option B says that It is possible that both Ellen and Lois are mistaken about Shirley's children.

Actually, no matter what Ellen and Louis say (you can forget about the passage also), this statement is always true. Because it is always "possible" for any two statements to be mistaken together. (Try to think of a situation where it is not even possible for both of them to be mistaken) There really is no need of any assumptions or premises, this statement always holds (only exception is when one says X is true and other says Not X is true).

S, if we say that option B must be true for this exchange, we are not really concluding anything.

Due to such a general nature of option B, I ignored it.

Option C says that:
Either Ellen is right about Shirley's children, or Lois is right about them, but they cannot both be right.

It says that both cannot be right together, which is true if the given assumption holds. Besides, it also leaves room for "both can be wrong". While some of the people have argued that option C means that one of E and L has to be correct, I don't agree.

As per Merriam Webster dictionary, either or means: (http://www.merriam-webster.com/dictionary/either-or)
an unavoidable choice or exclusive division between only two alternatives.

So, here if "either or" only means exclusive choice, not the unavoidable one, then both of them can be wrong.

Thus, option C is correct.

If anyone has any questions, please feel free to ask.

Regards,
CJ
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