An argument is invalid if and only if all the premises is true and the conclusion is false.
We can test the invalidity of the argument by assuming all the premises are true and seeing whether it is possible for the conclusion to be false. If the conclusion is possible to be false, then, the argument is invalid.
A valid argument, on the other hand, is valid if and only if it is necessary that:
1) if all of the premises are true, then the conclusion is true
2) if all of the premises are true, then the conclusion must be true
3) it is impossible that all the premises are true and the conclusion is false.
The authors purpose suggested by the text is explain how to use the guitar because it's not trying to convince you to buy a guitar and it isn't teaching you about all the parts on the guitar just how to tune the strings. Hope you found this helpful!
Contrast is the right answer for the question
The answer is A. Mercedes threw Andrea, Mercedes' best friend, a surprise party last night. This choice uses an appositive ("Andrea, Mercedes' best friend,") to combine the two sentences. An appositive is a phrase separated from the rest of the sentence by commas that describes something (in this case Andrea).
Choices B and C are incorrect because the uses of the words "but" and "when" to combine the sentences do not make logical sense. Choice D is incorrect because it uses a comma to combine the sentences without a conjunction, creating a run-on sentence.
Hope this helps!
