in number 3 why isnt the sufficient negated ?

why isnt the second sentence chained in #1

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why isnt the necessary condition not negated

Is this not the part vs whole flaw? Thats why I chose D. It was hard for me to identify the shape of the argument so i went with flaw type

So I saw that this was a valid argument but I thought it was A-->B then /B --->/A. Which one of the valid arguments in the syllabus is this

I thought you could negate some with all or none